Add host filtering for test_aggregate_add_existent_host and test_aggregate_remove_host_as_user tests

The resource_setup method is allocating all available compute
hosts as potential candidates, but in certain scenarios only
a subset of hosts should be acceptable. This patch filter out
hosts for those scenrios based on CONF.compute.target_hosts_to_avoid

Change-Id: Ie8886092e4e79eec164a3fe1939ea504200ea36b
1 file changed