enable linuxbridge for agent scheduler

Bug #1135793
blueprint quantum-scheduler

In addition, we refactor agent scheduler so that we will make
it easier to enable plugin to support agent scheduler.

Change-Id: I0d5cc8bcea644720a3c5cbe92486ce8d8ecd248c
NEC plugin support for dhcp network and router scheduling

blueprint quantum-scheduler

Change-Id: Icc1e4213cb6109ec82f4d438e277bd870c02729e
Merge "enable linuxbridge for agent scheduler"
Merge "NEC plugin support for dhcp network and router scheduling"