EnginePoll/EngineEpoll: fix polling timeout (#354)

* EnginePoll: Force the timeout to be exactly -1 when is negative. The
  implementation of the poll() system call in some OSes, including macOS
  and BSDs, throws an error for arbitrary negative values besides -1.
* EngineEPoll: apply the same fix for coherence and to avoid similar
  issues in the future.
* EnginePoll/EngineEPoll: remove the added millisecond to the timeout,
  when timeo is 0 is ok to pass 0 as timeout to the poll() methods to
  return without blocking triggering any pending events.

Fix #353

lib/ClusterShell/Engine/EPoll.py

@@ -114,7 +114,12 @@ def runloop(self, timeout):
                     timeo = timeout
 
                 self._current_loopcnt += 1
-                evlist = self.epolling.poll(timeo + 0.001)
+
+                if timeo < 0:
+                    poll_timeo = -1
+                else:
+                    poll_timeo = timeo
+                evlist = self.epolling.poll(poll_timeo)
 
             except IOError as ex:
                 # might get interrupted by a signal

lib/ClusterShell/Engine/Poll.py

@@ -109,7 +109,12 @@ def runloop(self, timeout):
                     timeo = timeout
 
                 self._current_loopcnt += 1
-                evlist = self.polling.poll(timeo * 1000.0 + 1.0)
+
+                if timeo < 0:
+                    poll_timeo = -1
+                else:
+                    poll_timeo = timeo * 1000.0
+                evlist = self.polling.poll(poll_timeo)
 
             except select.error as ex:
                 # might get interrupted by a signal