NVP plugin support for dhcp network scheduling

blueprint quantum-scheduler

Note: since NVP already support scale-out + high availability for L3
this only implements scheduling for dhcp.

Also, we do not expose the API extension, just use the internal
auto-scheduling.

Change-Id: Ifd29439fd463972ae085e5d28ed1893f94f2a2d8
Merge "NVP plugin support for dhcp network scheduling"