Fix old unicorn master not quitting after the new process is running
Fixes https://gitlab.com/gitlab-org/takeoff/issues/58
Follows https://bogomips.org/unicorn/SIGNALS.html advice to:
If "preload_app" is true, then application code changes will have no effect; USR2 + QUIT (see below) must be used to load newer code in this case.
Edited by GitLab Release Tools Bot