Implement VM rollback

Closes #184

api-daemon/pvcapid/helper.py

@@ -813,6 +813,30 @@ def remove_vm_snapshot(
     return output, retcode
 
 
+@ZKConnection(config)
+def rollback_vm_snapshot(
+    zkhandler,
+    domain,
+    snapshot_name,
+):
+    """
+    Roll back to a snapshot of a VM.
+    """
+    retflag, retdata = pvc_vm.rollback_vm_snapshot(
+        zkhandler,
+        domain,
+        snapshot_name,
+    )
+
+    if retflag:
+        retcode = 200
+    else:
+        retcode = 400
+
+    output = {"message": retdata.replace('"', "'")}
+    return output, retcode
+
+
 @ZKConnection(config)
 def vm_attach_device(zkhandler, vm, device_spec_xml):
     """