Make compute_capabilities_filter use information from DB not RPC

Make compute_capabilities_filter directly use the data in host_state and
not the data capabilities data that is currently broadcast from the
schedulers over RPC, as this will be removed since it doesn't scale.

The filter name, compute_capabilities_filter, is kept the same to keep
backwards compatibility.

This is a second attempt at this patch the first one broke the ability
to filter an arbitrary key value pairs, this time that is supported via
host_state.stats, along with tests to confirm

Once all the capabilities usage in scheduler filters is removed, the
capabilities RPC broadcast can be removed.

Part of bp no-compute-fanout-to-scheduler.

Change-Id: I0b9b05a25a8c1841093913c4a2fb19b48aff2ae1
Merge "Make compute_capabilities_filter use information from DB not RPC"