Move traits from "high" to "essential" priority
Move traits from "high" to "essential" priority

During the weekly Ironic meeting on 11-Dec-2017 it was decided that
the traits work was an essential priority, since in Rocky release,
nova is planning on replacing the ComputeCapabilitiesFilter with the
traits processing in placement API.

Added mgoddard as a contact as they have agreed to work on the code.

Change-Id: Ibc5e333f7f29ba51c1d63f226ab7703b6c3bdc7f

openstack/ironic-specs