Re Fix test_rebuild_server test by waiting for floating ip

It was originally attempted to be fixed in [1][2] but
the issue is still observed as fip wait was done
on wrong server instead the one created as part of test.

[1] https://review.opendev.org/c/openstack/tempest/+/814085
[2] https://review.opendev.org/c/openstack/tempest/+/828245

Closes-Bug: #1945495
Change-Id: I25b553e547baece65223ba884ef440fca65e5b64
1 file changed