Bug 884863: nova logs everything to syslog twice
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

n0ano/ganttclient