Also add the --headless option to make sure Gerrit isn't even trying
to serve the UI.
For historical reasons, http daemon wasn't enabled in the slave mode.
A reason for that is that, in Gerrit's early versions, it wasn't
possible to both run the http daemon and not serve the UI.
Slaves are read-only and disposable. They are used for two purposes:
* reduce latency on remote sites
* off-load clone/fetch traffic from Gerrit master
Git/HTTP is the best protocol to allow a flexible allocation of slaves,
because supports proxying and URL-based redirection.
Change-Id: Ic5568b4e8e005d660a9f61931831c39d270a9ef1
34001e4dbe