Move queue_get_for() from db to rpc.

Move queue_get_for() from db to rpc.

Part of blueprint common-rpc.

The function queue_get_for() is a utility function used by various
consumers of the rpc API.  This function lived in the db API, but never
ended up using anything from the database.  This patch moves it into the
rpc API so that it can be used by other users of rpc once it moves into
openstack-common.

Change-Id: If92675beecff5471b416a929c161b810e3c71939
Reviewed-on: https://review.openstack.org/9906
Reviewed-by: Vish Ishaya <vishvananda@gmail.com>
Approved: John Griffith <john.griffith@solidfire.com>
Tested-by: Jenkins