Make sure fixed IPs are different for multitenancy tests

We create two instances in different networks with same CIDR and
it may be possible that two instances will share same IP, as result
verify_connectivity will also show True as we will try to ping
our own IP address from the server.

Change-Id: I9d804c7a032aa31b93baad75c2311048f6f9a92d
1 file changed