multitenancy: Don't use fixed IPs in the test

Currently used fixed IPs didn't work on cloud with HA controllers as one
of IP addresses collided with an address assigned to DHCP port. This
patch removes fixed IPs and lets Neutron to assign IP to booted
instances. Later, those addresses are taken from server response and
reused.

Story: 2004330
Task: 27913

Change-Id: I3335ae43c17298f48cf869553e393df9ba7a070b
1 file changed