lbaas on a network without gateway

Not only check the gateway_ip in subnet, but also
check the host_routes. If there is a default route in host_routes
then the next hop of the default route is also a gateway_ip.

Closes-Bug: 1300017
DocImpact

Change-Id: Id3ae04bfa6cefb1c030857894f0594828b8e856d
Fix H302 violations

H302 violation is reported by flake8 when importing separated objects from
modules instead of importing the whole module.
e.g.   from package.module import function
       function()
is changed to
       from package import module
       module.function()

Change-Id: Ifbf31b52316d3cade40743752a49ce700f384a21
Closes-Bug: #1291032
Remove explicit dependency on amqplib

kombu already depends on amqp or amqplib depending on its
version, and no explicit access to amqplib exists in neutron code.

Closes-Bug: #1317094
Change-Id: I5cf189d7173b732cba6df3f9b6aff1d2bb85cdfe
Start ping listener also for postgresql

Make use of the automatic connection disposal for
PostgreSQL as well.

oslo-incubator commit: 4a591eaafe035fa3fd508c910f057bfa8ff51005

Change-Id: I6e6adb612968639dbc8deae31e5409aac44e340e
Closes-Bug: 1288438
Merge "Start ping listener also for postgresql"
Merge "Remove explicit dependency on amqplib"
Merge "Fix H302 violations"
Merge "lbaas on a network without gateway"