Correctly exit sway on errors.

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.

swaymsg/main.c

@@ -11,8 +11,8 @@
 #include "readline.h"
 #include "log.h"
 
-void sway_terminate(void) {
-	exit(EXIT_FAILURE);
+void sway_terminate(int exit_code) {
+	exit(exit_code);
 }
 
 int main(int argc, char **argv) {