The call to get_subnet_ids_on_router can return an empty list.
If the subnet_ids list is empty, the subsequent call to get
the ports on a subnet returns all ports. If this occurs
when doing a remove_router_interface, the performance
of a remove_router_interface degrades significantly. This change
returns immediately from check_ports_exist_on_l3agents if no
subnet is found. A new unit test has been added to cover
the specific case of returning immediately without calling
get_ports when a remove_router_interface operation is performed.
This allows the DVR job on stable/juno to go back to normal.
Conflicts:
neutron/tests/unit/test_l3_schedulers.py
Change-Id: I247d3bae152ab4f8ab7e00bd24d878eb08dca1ba
Closes-Bug: #1420032
Depends-On: I15bbf16fd4378c6431e9da8942d0968e7a012a91
(cherry picked from commit 760fe6a8fa)
96d472d732