Use oslo.utils

oslo.utils library now provides the functionality previously in
oslo-incubator's excutils, importutils, network_utils, strutils
timeutils, units etc. Some modules already moved to oslo.utils
will still be around since other code in nova/openstack/common/
are using it and will be removed in a subsequent commit.

Change-Id: Idc716342535fdfa680963e0e073ddb46f5f1eb34
Merge "Use oslo.utils"