Merge branch 'make-real-user' into 'master'

Make real user

So troubleshooting errors is easier (can use sudo su instead of sudo -u everytime)

/cc @dzaporozhets

See merge request !2

doc/install/README.md

@@ -22,6 +22,8 @@ sudo cp /opt/gitlab-runner/doc/install/upstart/gitlab-runner.conf /etc/init/
 sudo service gitlab-runner start
 ```
+You can troubleshoot failing builds by logging in as gitlab-runner with: `sudo -su gitlab-runner`.
+
 The runner will write log messages via Upstart to
 `/var/log/upstart/gitlab-runner.log`.