qa: fix rename instance for non-lvm backed storage

The rename instance test performs an lvm-specific check for tags on the
instance volume. This should be in the future abstracted *inside* the
template class, and not explicitly called from qa.

This would allow other disks to perform the checks that make sense for
them. In the meantime though, we just make the same check only when the
backend storage for the instance is lvm-based.

Signed-off-by: Guido Trotter <ultrotter@google.com>
Reviewed-by: Bernardo Dal Seno <bdalseno@google.com>