This PS moves alertmanager to use the endpoints section and
lookups to set the ports it serves on.
Change-Id: I62108ca207f615d10d0b4385da204214b9aeae32
Adds additional flags to Alertmanager for the peer meshing. This
also adds a headless discovery service so each instance can
calculate the DNS names of its mesh peers on startup.
Change-Id: I2ba7f4aec88f73e6bc3ff31117973ebb4e85ceba