Use oslo_utils instead of deprecated oslo.utils

oslo.utils 1.2.0 has changed its namespace from oslo.utils to
oslo_utils, the old import style of oslo.utils still can work but
it is deprecated.

Change-Id: I8832259624f15a8040f6de35136db7dd6d217f02

ceilometer/event/converter.py

@@ -20,7 +20,7 @@ import os
 
 import jsonpath_rw
 from oslo.config import cfg
-from oslo.utils import timeutils
+from oslo_utils import timeutils
 import six
 import yaml