Add regression test for bug 1796737
Add regression test for bug 1796737

Change I0839470c4bcfb16590a0d87b306d683b059bf8a9 fixed
root disk reporting for volume-backed servers during
an instance claim which is used during server create
and unshelve. However, resize claims track usage a bit
differently so local_gb_used reporting of a volume-backed
instance is still wrong. This adds a test to exhibit the
bug during resize.

The test was copied and modified from original change:

  https://review.openstack.org/428505/

Co-Authored-By: melanie witt <melwittt@gmail.com>

Change-Id: Iff6dc19f7f9eae3b6350fe6db7c08901d33f53e1
Related-Bug: #1796737

mikalstill/nova,openstack/nova,mikalstill/nova,openstack/nova,mahak/nova,rahulunair/nova,klmitch/nova,rahulunair/nova,openstack/nova,mahak/nova,klmitch/nova,rahulunair/nova,mahak/nova,klmitch/nova,klmitch/nova,mikalstill/nova