Make sure the "ExecStop" command line blocks until ejabberd is actually
stopped. This prevents systemd from killing the ejabberd process(es)
immediately.
Also, let the "ExecStart" command line block until ejabberd's startup is
completed. This makes sure that services which depend on ejabberd
aren't started up too early.
The "reload_config" command doesn't work the way admins would typically
expect, so it shouldn't be exposed via systemd. Those who understand
the behavior can execute the command using ejabberdctl.
Admins might expect ejabberd to be able to access data below /home or
/tmp. For example, they might use those locations to dump/restore
Mnesia backups, or as a document root for mod_http_fileserver or
mod_http_upload.
Fixes#1297.
