Added DiscoveryInfo for memsql masters.
Added DiscoveryInfo for memsql masters.

Creates the following in the /master/state.json API for the corresponding task of the master that we can then use to update our DNS.

discovery: {
	labels: {
		labels: [{
			key: "cluster_name",
			value: "###cluster_name###"
		}]
	},
	name: "###host_ip###",
	ports: {
		ports: [{
			number: ###memsql_port####
		}]
	},
	visibility: "EXTERNAL"
}
memsql/memsql-mesos,memsql/memsql-mesos,memsql/memsql-mesos,memsql/memsql-mesos