Add parameter to install abiword optionally
Fix upgrade of etherpad installation

The variable etherpad_branch was not locally available within the setup class.
Fix service reload on every puppet run

Etherpad-fetch with it's fetch command always triggered a refresh of
Etherpad::setup, which is itself subscriped by the service etherpad. Now
the fetching command has been moved over into the onlyif of etherpad-upgrade.