Make Watchdog Signal Configurable

Allows configuring the watchdog signal (with a default of SIGABRT).
This allows an alternative to SIGABRT when coredumps are not desirable.

Appropriate references to SIGABRT or aborting were renamed to reflect
more liberal watchdog signals.

Closes #8658

src/core/kill.c

@@ -12,6 +12,7 @@ void kill_context_init(KillContext *c) {
         c->final_kill_signal = SIGKILL;
         c->send_sigkill = true;
         c->send_sighup = false;
+        c->watchdog_signal = SIGABRT;
 }
 
 void kill_context_dump(KillContext *c, FILE *f, const char *prefix) {