libvirtconnection: Fix _EventLoop.run if thread exited abnormally.

Previously if the event loop thread exited abnormally, the run variable
was left in wrong value. Now the variable is set back to False in this case.

Change-Id: I347c8eee0425ce22c3677059c6b9c68ede10f24c
Signed-off-by: Maor Lipchuk <mlipchuk@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/22908
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>
Reviewed-by: Nir Soffer <nsoffer@redhat.com>