SCVMM - Set the active snapshot for a VM

No active snapshot was visible from the UI for a VM, the reason was because the 'current' property of the snapshot was not being correctly set.

https://bugzilla.redhat.com/show_bug.cgi?id=1141180
Merge pull request #613 from bronaghs/scvmm_active_snapshot

SCVMM - Set the active snapshot for a VM