Support sd_notify so systemd users can use Type=notify

[jameshartig]

Jira Link: DB-1409
We pretty heavily rely on systemd's Type=notify to know when a service is failing during a deployment. Can sd_notify support be added to both the master and tserver to send READY=1 when it has started up and ensured the port is available, created the necessary data dirs, etc.

Other projects have added similar functionality but with various definitions of "ready":
hashicorp/consul#2121
MariaDB/server#26
cockroachdb/cockroach#6268