libvirt: Fix misleading debug msg "Instance is running"
libvirt: Fix misleading debug msg "Instance is running"

We were logging "Instance is running" after guest creation, but
before the instance is running. The log message we emit when the
instance is actually running is "Instance spawned successfully".

Change-Id: I53ef1fb6a612fc55fa60f3a50f8710c8bf5caba4

rahulunair/nova,mahak/nova,mikalstill/nova,mikalstill/nova,openstack/nova,phenoxim/nova,gooddata/openstack-nova,klmitch/nova,rahulunair/nova,phenoxim/nova,openstack/nova,klmitch/nova,gooddata/openstack-nova,gooddata/openstack-nova,mahak/nova,klmitch/nova,openstack/nova,mahak/nova,klmitch/nova,rahulunair/nova,mikalstill/nova,gooddata/openstack-nova