Use oslo.utils

oslo.utils library now provides the functionality previously in
oslo-incubator's excutils, importutils, network_utils, strutils
timeutils, units etc. Some of these outdated modules will still be
around for a while until all other oslo modules that use them have been
updated in future commits.

Change-Id: Idee8600dfe42e5977b8fb824e91afff7e9119981
Merge "Use oslo.utils"