QA: Use instance name for rename test

Reported in issue 341. In some setups the instance live in a different
netblock from the cluster. Therefore a the configuration-global “rename”
name shouldn't be used for them. Instead another instance name is used.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>