Adds support for managing services using s6

The ServiceManager can now stop, start, and restart services inside container that use
s6 to manage services.

The restart command sends a SIGKILL to the service and relies on s6 to restart the service.
This was needed because some services such as PostgreSQL shut down gracefully when SIGTERM
is sent. The graceful shutdown does not happen until all connections are closed by clients.
When testing Pulp, a graceful shutdown is not needed.

[noissue]

pulp_smash/cli.py

@@ -356,6 +356,8 @@ def _get_service_manager(cfg, pulp_host):
 
         client = Client(cfg, echo_handler, pulp_host=pulp_host)
         commands_managers = (
+            ("which s6-svc", "s6"),
+            ("test -x /bin/s6-svc", "s6"),
             ("which systemctl", "systemd"),
             ("which service", "sysv"),
             ("test -x /sbin/service", "sysv"),
@@ -392,6 +394,15 @@ def _start_systemd(client, services):
         cmd = ("systemctl", "start") + tuple(services)
         return (client.run(cmd, sudo=True),)
 
+    @staticmethod
+    def _start_s6(client, services):
+        return tuple(
+            (
+                client.run(("s6-svc", "-u", "/var/run/s6/services/{}".format(service)))
+                for service in services
+            )
+        )
+
     @staticmethod
     def _stop_sysv(client, services):
         return tuple((client.run(("service", service, "stop"), sudo=True) for service in services))
@@ -401,6 +412,15 @@ def _stop_systemd(client, services):
         cmd = ("systemctl", "stop") + tuple(services)
         return (client.run(cmd, sudo=True),)
 
+    @staticmethod
+    def _stop_s6(client, services):
+        return tuple(
+            (
+                client.run(("s6-svc", "-d", "/var/run/s6/services/{}".format(service)))
+                for service in services
+            )
+        )
+
     @staticmethod
     def _restart_sysv(client, services):
         return tuple(
@@ -412,6 +432,15 @@ def _restart_systemd(client, services):
         cmd = ("systemctl", "restart") + tuple(services)
         return (client.run(cmd, sudo=True),)
 
+    @staticmethod
+    def _restart_s6(client, services):
+        return tuple(
+            (
+                client.run(("s6-svc", "-k", "/var/run/s6/services/{}".format(service)))
+                for service in services
+            )
+        )
+
     @staticmethod
     def _is_active_sysv(client, services):
         with contextlib.suppress(exceptions.CalledProcessError):
@@ -427,6 +456,19 @@ def _is_active_systemd(client, services):
             return (client.run(cmd, sudo=True),)
         return False
 
+    def _is_active_s6(self, client, services):
+        def process_ps_output(command_output, service):
+            if command_output.stdout.find(service) > -1:
+                return True
+            else:
+                return False
+
+        with contextlib.suppress(exceptions.CalledProcessError):
+            return tuple(
+                (process_ps_output(client.run(("ps", "x")), service) for service in services)
+            )
+        return False
+
     @abstractmethod
     def start(self, services):
         """Start the given services.
@@ -527,6 +569,8 @@ def start(self, services):
                         result[host.hostname] = self._start_sysv(client, services)
                 elif svc_mgr == "systemd":
                     result[host.hostname] = self._start_systemd(client, services)
+                elif svc_mgr == "s6":
+                    result[host.hostname] = self._start_s6(client, services)
                 else:
                     raise NotImplementedError(
                         'Service manager "{}" not supported on "{}"'.format(svc_mgr, host.hostname)
@@ -552,6 +596,8 @@ def stop(self, services):
                         result[host.hostname] = self._stop_sysv(client, services)
                 elif svc_mgr == "systemd":
                     result[host.hostname] = self._stop_systemd(client, services)
+                elif svc_mgr == "s6":
+                    result[host.hostname] = self._stop_s6(client, services)
                 else:
                     raise NotImplementedError("Service manager not supported: {}".format(svc_mgr))
         return result
@@ -575,6 +621,8 @@ def restart(self, services):
                         result[host.hostname] = self._restart_sysv(client, services)
                 elif svc_mgr == "systemd":
                     result[host.hostname] = self._restart_systemd(client, services)
+                elif svc_mgr == "s6":
+                    result[host.hostname] = self._restart_s6(client, services)
                 else:
                     raise NotImplementedError("Service manager not supported: {}".format(svc_mgr))
         return result
@@ -597,6 +645,8 @@ def is_active(self, services):
                         result[host.hostname] = self._is_active_sysv(client, services)
                 elif svc_mgr == "systemd":
                     result[host.hostname] = self._is_active_systemd(client, services)
+                elif svc_mgr == "s6":
+                    result[host.hostname] = self._is_active_s6(client, services)
                 else:
                     raise NotImplementedError("Service manager not supported: {}".format(svc_mgr))
         return result
@@ -657,6 +707,8 @@ def start(self, services):
                 return self._start_sysv(self._client, services)
         elif self._svc_mgr == "systemd":
             return self._start_systemd(self._client, services)
+        elif self._svc_mgr == "s6":
+            return self._start_s6(self._client, services)
         else:
             raise NotImplementedError("Service manager not supported: {}".format(self._svc_mgr))
 
@@ -672,6 +724,8 @@ def stop(self, services):
                 return self._stop_sysv(self._client, services)
         elif self._svc_mgr == "systemd":
             return self._stop_systemd(self._client, services)
+        elif self._svc_mgr == "s6":
+            return self._stop_s6(self._client, services)
         else:
             raise NotImplementedError("Service manager not supported: {}".format(self._svc_mgr))
 
@@ -687,6 +741,8 @@ def restart(self, services):
                 return self._restart_sysv(self._client, services)
         elif self._svc_mgr == "systemd":
             return self._restart_systemd(self._client, services)
+        elif self._svc_mgr == "s6":
+            return self._restart_s6(self._client, services)
         else:
             raise NotImplementedError("Service manager not supported: {}".format(self._svc_mgr))
 
@@ -701,6 +757,8 @@ def is_active(self, services):
                 return self._is_active_sysv(self._client, services)
         elif self._svc_mgr == "systemd":
             return self._is_active_systemd(self._client, services)
+        elif self._svc_mgr == "s6":
+            return self._is_active_s6(self._client, services)
         else:
             raise NotImplementedError("Service manager not supported: {}".format(self._svc_mgr))