package/gitlab-runner: fix inconsistency of systemd and sysv daemons

Copy default $DAEMON_ARGS from systemd service to sysv init script.

Make GITLAB_RUNNER_USER home directory the same as default
--work-directory (-d) flag.

Run sysv daemon process using root user (remove -c option)
This is needed to correctly access config files as specified.
System access can still be limited with gitlab-runner `--user` flag.

Use same $DAEMON_ARGS variable name so it can be overwritten in
/etc/default/gitlab-runner environment file in both cases.

Signed-off-by: Marek Metelski <marek.metelski@grinn-global.com>
Reviewed-by: Marcin Niestroj <m.niestroj@grinn-global.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>