When tag calculation fails and the same tag is stopped as a side effect, we
don't try to update its value anymore.

New class RootDB has no parents and handles RPC calls to the cc-server in a
transparent fashion from its children.

All tags were announced with a ttl of None.

Was ignoring event 0 which is used to stop "polling" events.
Was using mapping which couldn't work with multiple events.

These jobs are needed for VM migration/clone.

JobManager + BaseJob.

When role changes in a new authentication attempt.
Was missing a method on MainLoop instance to unregister all plugins.

Tag that had infinite TTL and with a periodic refresh didn't had their
registration done in case off None -> not None value and vice versa.

Tag version was not registered.

Set rpc_con to False in restart_rpc_connection.

Libvirt raises an exception saying "domain not runnning" when trying to destroy
a VM that is in fact running. So we try to figure out if this is this kind of
exception and we ignore it in this case.

Only log error in case of error.

When VM is not started, vnc port value is -1 in the libvirt domain XML config.