Members that were disabled / admin_state_up=False were simply excluded
from the haproxy configuration we pass to the amps. Instead, we should
be creating them in a disabled state, so they return in health messages
as status "maint", and can be marked OFFLINE via the standard health
mechanism, instead of just via override hacks.
This also resolves a bug introduced in an earlier change:
https://review.openstack.org/#/c/567322/
which caused admin-downed members to stay in NO_MONITOR always.
Change-Id: I6615b3ff89d7cef2af52d474aab3a03d947f98be