Add '--install-plugin' option to init step

This allows automatically install given plugin without asking. Can be
also used together with '--batch' to automatically install/update Gerrit
without interactions.

Change-Id: I8e0cf8f2e39c813e54daff6b587cb8cd2485bae8
Signed-off-by: Dariusz Luksza <dariusz@luksza.org>
5 files changed