Fix a pylint false-positive error in the container.docker driver

pylint doesn't understand the docker_info lazy function return value as a dict.

(cherry picked from commit 885b76b)

opensvc/utilities/subsystems/docker.py

@@ -170,7 +170,7 @@ def docker_info(self):
         try:
             self.docker_exe
         except ex.InitError:
-            return ""
+            return {}
         cmd = [self.docker_exe, "info"] + self.json_opt
         try:
             data = json.loads(justcall(cmd)[0])
@@ -372,12 +372,11 @@ def _docker_info_drivers(self):
         Return the docker drivers keys conttributed to resinfo.
         """
         data = []
-        if "Driver" in self.docker_info:  # pylint: disable=unsupported-membership-test
-            # pylint: disable=unsubscriptable-object
-            data.append(["", "storage_driver", self.docker_info["Driver"]])
-        if "ExecutionDriver" in self.docker_info:  # pylint: disable=unsupported-membership-test
-            # pylint: disable=unsubscriptable-object
-            data.append(["", "exec_driver", self.docker_info["ExecutionDriver"]])
+        di = dict(self.docker_info) # dict cast to please pylint
+        if "Driver" in di:
+            data.append(["", "storage_driver", di["Driver"]])
+        if "ExecutionDriver" in di:
+            data.append(["", "exec_driver", di["ExecutionDriver"]])
         return data
 
     def _docker_info_images(self):
@@ -555,8 +554,8 @@ def __init__(self, svc=None):
         else:
             self.docker_pid_file = None
             try:
-                # pylint: disable=unsubscriptable-object
-                set_lazy(self, "container_data_dir", self.docker_info["DockerRootDir"])
+                di = dict(self.docker_info) # dict cast to please pylint
+                set_lazy(self, "container_data_dir", di["DockerRootDir"])
             except (KeyError, TypeError):
                 set_lazy(self, "container_data_dir", None)
 
@@ -797,9 +796,8 @@ def _docker_running_shared(self):
             }
         }
         """
-        if not self.docker_info.get("ServerVersion"):
-            return False
-        return True
+        di = dict(self.docker_info) # dict cast to please pylint
+        return di.get("ServerVersion") is not None
 
     def _docker_running_private(self):
         """