Refactor, simplify registration of built-in watchdog daemon

This patch not only greatly simplifies the registration of the built-in
watchdog daemon, it also fixes a nasty race condition with an external
watchdog daemon.  The INIT_CMD_WDOG_HELLO could reach finit in reversed
order, leading to the built-in daemon shutting down, but finit killing
the just registered external daemon.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

src/finit.c

@@ -390,7 +390,7 @@ int main(int argc, char* argv[])
 	/*
 	 * Start built-in watchdog as soon as possible, if enabled
 	 */
-	watchdog(argv[0]);
+	wdogpid = watchdog(argv[0]);
 
 	/* Set hostname as soon as possible, for syslog et al. */
 	set_hostname(&hostname);