Adding additional assertions for retype test
Adding additional assertions for retype test

This commit fixes the review comment of
https://review.openstack.org/#/c/572287/ to
add extra checks for destination volume type

Change-Id: Ie0f4bd7e69f83e83846e5e281c7bd121c584992e

masayukig/tempest,openstack/tempest,cisco-openstack/tempest,cisco-openstack/tempest,openstack/tempest,masayukig/tempest