Implements support migration for volume transfer

Implements support for the volume transfer api added to cinder in
https://review.openstack.org/#/c/29227

Change-Id: Idbcdfdd3ef76a8c516e08d1cf351d549254bc8c0
python3: Strutils is not needed

strutils is used to safely encode and decode unicode strings
for python2.7. Since unicode strings are the default in python3,
ignore the use of strutils when running with python3.

Change-Id: I9a8e296b4f2153b1ef4302a7dcd797fbb4561c35
Signed-off-by: Chuck Short <chuck.short@canonical.com>
Merge "Implements support migration for volume transfer"
Merge "python3: Strutils is not needed"