some corrections in install file and rc.d/systemd files

Following points are addressed with this commit:
* According to the arch policy to switch to systemd, the rc.d file is now obsolete. So I removed the file.
* The correct install location of the gerrit.service is /usr/lib/systemd/system and not etc - according to arch systemd rules
* Java-runtime dependencies adjusted, as it needs ttf-dejavu and libcups to successfully execute on a server (headless) system...
* gerrit.install adjusted to be kind of generic and customizable by setting some things at the top of the file.

Most of the changes were proposed to me as maintainer of the jenkins-ci package so I thought they should be adjusted here too.