Hack vswitchd init script to remove bridge ports at startup

Hack vswitchd init script to remove bridge ports at startup

XAPI will recreate all the bridges and reconnect the interfaces at
startup, so this is safe in the Xen environment.  If we don't do this
stale vifs hang around in the configuration file.

This is a hack and not a true solution because it doesn't handle
port-related configuration, etc.  A better solution needs to be
implemented in the future.