Remove tempest_auto_config script

This script isn't being used by anyone to my knowledge nor has it
really been maintained since it was first added. We will be working
on a plan for automating tempest configuration soon and this
doesn't really fit the initial set requirements of requirements. It
also does not have any testing, so I expect that it has bit rotted
and probably doesn't work anymore.

Change-Id: Id896d9877312dfb6b12b54ea1c598a1940cdd9ce
Get credential IDs from Credentials class

With the move to Credentials class, tenant_id and user_id are
available in the Credentials instance.
Several test use identity admin client to obtain tenant_id
and user_id, fixing them to get the IDs from Credentials instead.

Partially implements: bp multi-keystone-api-version-tests

Change-Id: I8c38fb8d191a88fab37633c6edffd54492c41fd5
Merge "Remove tempest_auto_config script"
Merge "Get credential IDs from Credentials class"