core: fix commit snapshot flow on active vm commit

* RestoreAllSnapshotsCommand -> getSnapshot method:
- COMMIT branch: get IN_PREVIEW snapshot by status.

* SnapshotDao:
- Added a new getter for fetching snapshots only by status.

* snapshot_sp.sql:
- Added GetSnapshotByVmIdAndStatus stored procedure.

Change-Id: Ib27d225b7bf584f1d0c6e2861e91403ba205f087
Bug-Url: https://bugzilla.redhat.com/1093047
Signed-off-by: Daniel Erez <derez@redhat.com>