Add volume migrate action

This patch adds volume migrate action.

Change-Id: I9f46931d2a7edff4c727d674ec315924b9ae30c2
Implements: blueprint volume-migrate-action

watcher/common/utils.py

@@ -17,7 +17,9 @@
 """Utilities and helper functions."""
 
 import datetime
+import random
 import re
+import string
 
 from croniter import croniter
 
@@ -158,3 +160,8 @@ StrictDefaultValidatingDraft4Validator = extend_with_default(
     extend_with_strict_schema(validators.Draft4Validator))
 
 Draft4Validator = validators.Draft4Validator
+
+
+def random_string(n):
+    return ''.join([random.choice(
+        string.ascii_letters + string.digits) for i in range(n)])