util.startup: Fix exiting on pidfile trouble prosody.shutdown() relies on prosody.main_thread, which has not been set yet at this point. Doing a clean shutdown might actually be harmful in case it tears down things set up by the conflicting Prosody, such as the very pidfile we were looking at. Thanks again SigmaTel71 for noticing

For full information on our dependencies, version requirements, and
where to find them, see https://prosody.im/doc/depends

If you have luarocks available on your platform, install the following:

  - luaexpat
  - luasocket
  - luafilesystem
  - luasec