Introduce the 'force-start' option in snf-ganeti-eventd init script.
When invoked with force-start snf-ganeti-eventd will start regardless
the node's role or the default settings. It will start:

 * even if the host is NOT the Ganeti master
 * even if snf-ganeti-eventd is NOT enabled in the defaults file

'force-start' should be used only during the preparation of a node to
become a Ganeti master a.k.a during a master-failover.