Replace an instance of keystone/openstack/common/timeutils

There was an instance of timeutils from the sycn'ed code in:
keystone/contrib/federation/idp.py, we should replace is with
oslo.utils.

Change-Id: I5a208903d6810d8f2d43fc710874f6d8463e2150
Merge "Replace an instance of keystone/openstack/common/timeutils"