unskip test_list_servers_filtered_by_ip

Bug #1170718 is fixed, so we can unskip the test_list_servers_filtered_by_ip.
Also making the test compatible with tenant+network isolation settings.

Change-Id: I31ec6baac41a084b2106bef2fb686030ba599c7f
Merge "unskip test_list_servers_filtered_by_ip"