libvirtconnection: Fix a race when starting the eventloop

This patch fixes a race which occurs when setting self.run to True
only after starting the thread.

Signed-off-by: Maor Lipchuk <mlipchuk@redhat.com>
Change-Id: I7cad0adfdd6c10e173888ee95ef822e1a62f7767
Reviewed-on: http://gerrit.ovirt.org/22859
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>
Reviewed-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-by: Francesco Romani <fromani@redhat.com>