Use Heat resource to validate resource_type_show
Use Heat resource to validate resource_type_show

Patch I01aaadf86bf86f2a01bfd3fd28541522ef5a99cf added new functionality,
which raise error, if resource related endpoint is not registred in
keystone. Due to heatclient functional tests job starts only heat and
keystone service, we should use Heat resources for testing. The good
candidate for it is OS::Heat::RandomString.

Change-Id: I274a6db5c886ce8e19968e6e2ae8b16e93315cb7
Closes-Bug: #1482661

ecerulm/python-heatclient,openstack/python-heatclient,ecerulm/python-heatclient