Replace datetime.utcnow with timeutils.utcnow

Fixes bug #1008064

Replaced datetime.utcnow usage with timeutils.utcnow

Change-Id: I8bfdc1abefc3891497554335a3078d4028ef8ac9

openstack/common/timeutils.py

@@ -30,7 +30,7 @@ TIME_FORMAT = "%Y-%m-%dT%H:%M:%S"
 def isotime(at=None):
     """Stringify time in ISO 8601 format"""
     if not at:
-        at = datetime.datetime.utcnow()
+        at = utcnow()
     str = at.strftime(TIME_FORMAT)
     tz = at.tzinfo.tzname(None) if at.tzinfo else 'UTC'
     str += ('Z' if tz == 'UTC' else tz)