taskdistribution: fix wrong calculation of watcher sleeps

There was a sign error in the formula and it lacks code to deal with clock
changes.
Because the watcher will be removed, this patch reverts to imprecise but safe
and simple implementation.

erp5/util/taskdistribution/__init__.py

@@ -317,7 +317,6 @@ class TestResultProxy(RPCRetry):
     def _watcher(self):
         cond = self._watcher_condition
         while self._watcher_can_run and self.isAlive():
-            working = time.time()
             caption_list = []
             append = caption_list.append
             for name, (stream, max_history_bytes) in \
@@ -341,8 +340,7 @@ class TestResultProxy(RPCRetry):
                 append(caption)
             self.reportStatus('', '\n'.join(caption_list), '')
             with cond:
-                cond.wait(max(self._watcher_period - (working - time.time()),
-                    0))
+                cond.wait(self._watcher_period)
 
     def _stopWatching(self):
         cond = self._watcher_condition