fix(*): Announce the published port to etcd

Announce the external instead of the internal port to etcd. Currently
all components are using the same internal and external port, so this
never broke deis.
Before publishing etcd, scan whether the internal port is opened
Builder listens on 22 (internal) and is published on 2223
chore(*): Rename PUBLISH to EXTERNAL_PORT

This makes the boot logic more understandable. This commit also fixes
some wrong comments, about what is published and what is checked.
chore(cache): Remove moved systemd unit file
Merge pull request #1864 from johanneswuerbach/announce-correct-port

fix(*): Announce the published port to etcd