Added systemd unit file and gitlab-runner config

Makefile

-all:
+all: gitlab-runner-config gitlab-runner-service
 	mkdir -p ../go/go/src/gitlab.com/gitlab-runner
 	mkdir -p ../go/gocache
 	tar xf gitlab-runner-v13.1.0.tar.gz -C ../go/go/src/gitlab.com/gitlab-runner
@@ -7,3 +7,35 @@ all:
 	cd ../go/go/src/gitlab.com/gitlab-runner/gitlab-runner && install -D -m 755 out/binaries/gitlab-runner /usr/bin/gitlab-runner
 	rm -rf /usr/local/share/.cache
 	rm -rf ../go/gocache
+	install -m755 -d /etc/gitlab-runner
+	@echo "$$GITLAB_RUNNER_CONFIG" > /etc/gitlab-runner/config.toml
+	@echo "$$GITLAB_RUNNER_SERVICE" > /lib/systemd/system/gitlab-runner.service
+	systemctl enable gitlab-runner.service
+
+gitlab-runner-config:
+define GITLAB_RUNNER_CONFIG
+concurrent = 1
+check_interval = 0
+
+[session_server]
+  session_timeout = 1800
+endef
+export GITLAB_RUNNER_CONFIG
+
+gitlab-runner-service:
+define GITLAB_RUNNER_SERVICE
+[Unit]
+Description=GitLab Runner
+After=syslog.target network.target
+
+[Service]
+StartLimitInterval=5
+StartLimitBurst=10
+ExecStart=/usr/bin/gitlab-runner run --working-directory /var/lib/gitlab-runner --config /etc/gitlab-runner/config.toml --service gitlab-runner --syslog --user root
+Restart=always
+RestartSec=120
+
+[Install]
+WantedBy=multi-user.target
+endef
+export GITLAB_RUNNER_SERVICE