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.

In case of an exception, the value of the tag is set to None.

When doing remote execution, it was sometimes failing with the following
exception: OSError: [Errno 10] No child processes.
The problem is when using libev default loop, the latest register a handler for
SIGCHLD, it causes a problem when Popen.communicate() tried to do a wait_pid,
the syscall is skipped because of the signal. Then when wait_pid is called
again, it failed because the process don't exist anymore.

Some tags were returning None because of bad decorator.