change unicorn timeout to 300

I'm not entirely sure this is necessary however I've been getting lots of 502 errors recently that seem to relate to timeout values. Can someone elaborate on what other things could be affected by this timeout value being low or high?

Can someone explain why the Unicorn timeout does not match the `nginix` [`proxy_connect_timeout`](https://github.com/gitlabhq/gitlabhq/blob/0718d877b9b2ee9a8acd22e3c6d5abed2a5e9639/lib/support/nginx/gitlab#L64)?

Additionally can someone explain [`satellites` -> `timeout`](https://github.com/gitlabhq/gitlabhq/blob/0718d877b9b2ee9a8acd22e3c6d5abed2a5e9639/config/gitlab.yml.example#L201) in `gitlab/yml`?

/cc @Razer6 @randx @dosire