Cleanup rename of get_compute_ports_on_host_by_subnet

A recent merge [1] renamed this method to remove "compute_" from the
name.  Unfortunately, the rename was not done thoroughly.  This patch
cleans that up.  No bug is referenced since this is an obvious
ommission in a recent patch.

[1] https://review.openstack.org/#/c/114141/

Change-Id: I8320bc8deb6dcda586ccff01120270b3ce257ea2
Add scheduler unit tests to enable bug fixes and refactoring

Improves the coverage for DVR scheduling and will allow safer bug
fixes and refactoring in follow-on patches.

Change-Id: I02d0126e31adcab88a7ee82ba1cb76f952c9a68c
Partial-bug: #1353266
Partial-bug: #1356639
Co-Authored-By: Swaminathan Vasudevan <swaminathan.vasudevan@hp.com>
Co-Authored-By: Carl Baldwin <carl.baldwin@hp.com>
Remove subnet_id from check_ports_exist_on_l3agent

Refactor check_ports_exist_on_l3agent so that subnet_id no longer
needs to be passed.  Instead it calls get_subnet_ids_on_router.  This
helps to pave the way for removing hints from schedule router.

Partial-bug: #1353266
Partial-bug: #1356639
Co-Authored-By: Swaminathan Vasudevan <swaminathan.vasudevan@hp.com>
Co-Authored-By: Carl Baldwin <carl.baldwin@hp.com>

Change-Id: I6e9dcb0b899294bb4cf3e3d616a0a690049c338e
Call unbind_snat_servicenode from schedule router

Refactor to move the call to plugin.unbind_snat_servicenode from
schedule_snat_router to _schedule_router.  This is a move to pave the
way for removing hints from schedule router.

Partial-bug: #1353266
Partial-bug: #1356639
Co-Authored-By: Swaminathan Vasudevan <swaminathan.vasudevan@hp.com>
Co-Authored-By: Carl Baldwin <carl.baldwin@hp.com>

Change-Id: I062d8cc3cb870bbaa033d5b107a7dd868dfafa19
Remove hints from schedule_router

Partial-bug: #1353266
Partial-bug: #1356639
Co-Authored-By: Swaminathan Vasudevan <swaminathan.vasudevan@hp.com>
Co-Authored-By: Carl Baldwin <carl.baldwin@hp.com>

Change-Id: Ie6b55e5d0d70be74b19c91994e52eb1719e32fef