Calling `exit` in sway_terminate prevents sway from correctly shutting
down (freeing data, cleanly terminating the ipc server, etc.).
A better way is to exit straight away if the failure occurs before
`wlc_run` and use sway_abort as usual if it occur when wlc is running.
Using 'flag' results in duplicate code paths for short and long options.
This broke the -q short option in swaymsg, because there was:
{"quiet", no_argument, &quiet, 'q'}
Which will set quiet to 'q' and return 0, not 'q'.
