Nova service plugin for OpenStack Searchlight

Nova services should be indexed. And nova already supports versioned notifications for service.

Support set vgamem for video for OpenStack Compute (nova)

We can set video.vram by setting hw_video_ram in image properties currently [1], but can't set vgamem. The default vgamem is 16MiB, it's not enough for 4k resolutions in some cases. [2] [1]: https://github.com/openstack/nova/blob/master/nova/virt/libvirt/driver.py#L4170-L4177 [2]: http://www.ovirt.org/documentation...

add notification for compute node for OpenStack Compute (nova)

Currently, no notification will be sent for hypervisor(compute node) state change, so it is not possible for external system like searchlight to get notification when there are hypervisors created/updated/deleted.