gerrit.sh uses su to invoke gerrit as $GERRIT_USER without specifying a shell; thus, if $GERRIT_USER's default shell is anything other than /bin/sh (or something compatible like bash), in particular if it's /sbin/nologin or /bin/false, the script would fail to launch gerrit. Explicitly setting a shell when launching Gerrit fixes this. Change-Id: I986ca438676d7cdec4437ddd286ba3af2ee39388