Fix invalid call to exit/2 in couch_server
Previously we called it as `exit(couch_server_N, config_change)` but exit/2
doesn't know what to do with an atom, it needs a pid.
```
exit(couch_server_1, foo).
** exception error: bad argument
in function exit/2
called as exit(couch_server_1,foo)
*** argument 1: not a pid
```
This doesn't actually restart the servers as intended and it's also making
quite a mess in the eunit logs.
In addition to ensuring we're calling a Pid, use a `{shutdown, _}` error shape
to avoid triggering verbose SASL report as it's an expected condition.
1 file changed
