libvirtconnection: ping libvirt upon disconnection

Upon recieving an error from libvirt we should ping it
(using getLibVersion) and only upon failure treat it as down.

Libvirt error codes do not distinguish recoverable from non-recoverable
libvirt errors.

Change-Id: Ia489e46dd8ce4c70c888988d17b86311d3c4b935
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=982634
Signed-off-by: Mooli Tayer <mtayer@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/19444
Reviewed-by: Saggi Mizrahi <smizrahi@redhat.com>
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>