Refactor fallback shell handling, run as regular service

This patch re-enables the fallback shell handling after the big TTY
refactor.  We do this by allowing the fallback shell to run as a
regular service.

Note: this also adds the "hidden" support for 'notty' option for
      tty configurations stanzas.  This is just to pick up from
      where the kernel left us, reusing stdin + stdout.

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

src/conf.c

@@ -737,6 +737,10 @@ int conf_reload(void)
 
 	globfree(&gl);
 
+	/* Verify config, do we have at least one TTY available? */
+	if (tty_fallback(FINIT_CONF))
+		logit(LOG_WARNING, "warning, no getty enabled on local TTYs.");
+
 	/* Mark any reverse deps as chenaged. */
 	service_update_rdeps();