Do not import openstack.common.log in strutils

strutils imports openstack.common.log that depends on
notifier, rpc, eventlet, etc. This import was inherited
from old utils.py and is not used in strutils.

All these numerous dependencies are not desirable in such
small projects as novaclient that needs strutils only.

Change-Id: I7761fb53ab58bd8801448c56648dace14ca7dc89
Fixes: bug #1174215