Remove a DB query for get_ports_by_node()

This renames get_ports_by_node() to get_ports_by_node_id() and changes
the node_id argument to always need to be the integer ID. This removes
the need for get_ports_by_node() to query the DB for UUID -> ID
conversion.

By doing this, we can save a DB query in the cases where we already have
the Node integer ID.

This is needed to help set up the next patch to clean up calls to
get_node(). There's now a case in port API controller where we need
to lookup the Node by UUID just to get its ID to be passed into this
call. Until we implement the Node lazy-loading code, we fetch the
full Node, but this isn't any worse than before for this case, as
I'm just moving it from the DB layer. I've noted this with a FIXME
and it will be made more efficient in the future.

Change-Id: I9993c0c87794171fb971524ac5c30490b3e33716
Merge "Remove a DB query for get_ports_by_node()"