Store CONF.baremetal.instance_type_extra_specs in DB

The baremetal driver supports sending back arbitrary key value pairs via
RPC for scheduling purposes.  Since the rpc fanout is being removed
store these values in the database in the ComputeNodeStat table.

A separate patch will update the compute_capabilities_filter to use
these values.

part of bp no-compute-fanout-to-scheduler

Change-Id: I03d20484cd78f9cd64dcc3d270b2882c6ab12195
Merge "Store CONF.baremetal.instance_type_extra_specs in DB"