pep8 cleanup
Added tenant_id as argument to allocate_ip_address
Removed redundant code.
Added test for subnet selection on ip allocation.
Added test for net_id filter on new ip address allocation.
Added test for net_id filter on deallocated ip address allocation; fixed bug in previous test.
Refactored test with _create_and_insert_net
Refactored test with _create_and_insert_subnet
Refactored test with _create_and_insert_port
Refactored test with _create_and_insert_ip