Simplify instance rename qa test

The current instance rename qa testing function can only perform
back-and-forth renames, both for command line and rapi. In order to be
able to perform same-name rename tests we change it to be able to
perform simple renames, and then we change qa to call it to perform both
sides of the renaming.

The same change is applied both to the local and the rapi test.

Signed-off-by: Guido Trotter <ultrotter@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>