Handles correctly termination.

Clean authentication code.

This is a fix when is the same poll we try to update a tag value for a VM and
the domain just has been removed.

Needed for disk synchronisation during live migration.

Type is the same as returned by libvirt (for now).
One of dir, fs, netfs, logical, disk, iscsi, mpath, rbd.

Harmless renaming.

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.