Bug 884863: nova logs everything to syslog twice

Fix double-registration of the syslog handler.
NovaRootLogger.setup_from_flags is called twice from log.setup() -- once
through NovaRootLogger.__init__ and once through reset().  setup_from_flags
wasn't idempotent, so this resulted in the syslog handler being registered
twice.

Rather than fix the twisty-turny maze that is setup(), I've opted to make
setup_from_flags idempotent in this regard, by always unregistering the
syslog handler before doing anything else.

Change-Id: I59ad61751e1a19d2cbb73dc1deea9c708d4c5032

nova/log.py

@@ -245,11 +245,12 @@ class NovaRootLogger(NovaLogger):
     def setup_from_flags(self):
         """Setup logger from flags."""
         global _filelog
+        if self.syslog:
+            self.removeHandler(self.syslog)
+            self.syslog = None
         if FLAGS.use_syslog:
             self.syslog = SysLogHandler(address='/dev/log')
             self.addHandler(self.syslog)
-        elif self.syslog:
-            self.removeHandler(self.syslog)
         logpath = _get_log_file_path()
         if logpath:
             self.removeHandler(self.streamlog)