Adds "retype" to "volume/admin/test_volume_types.py"

This submission is to verify "retype"  functionality.
Updates existing testcase under
"tempest/api/volume/admin/test_volume_types.py" to
"test_create_update_get_delete_volume_with_volume_type",
and also added required support functions.

Change-Id: I766f39e6afe1d318469677963c4e9bbba4e44ad0
2 files changed