Add oslo.utils requirement

With the release of oslo.utils, keystoneclient can make use of it
rather than using the functions in oslo-utils.

Change-Id: I1b5392f10f8b67c9c3ac3bc3d2dd06ea08417aa6
Use oslo.utils

keystoneclient was using utility function from oslo-incubator
rather than oslo.utils.

Change-Id: I2909a2150b9556e54ef88e72358fda1cf8b7cc1c
Merge "Add oslo.utils requirement"
Merge "Use oslo.utils"