Unit test for resource attribute SHOW fix

The change https://review.openstack.org/#/c/140766 was merged before a
previous version of this patch (for bug 1400557), but didn't have any
unit tests.  I've removed the fix but left the unit test here.

Closes-Bug: #1401107
Change-Id: I788c181ce55f076243f9bbdf791289a5f45c3758
Merge "Unit test for resource attribute SHOW fix"