Snmpsim fail when it fails (#8392)

* Update snmpsim to fail better if it can't be started.
The main issue is the isRunning() check was done too soon after forking, the sh process was still running.

* increase default delay to 2s

* Pull this back, all we need is the sleep really.

* Remove removed exception

tests/bootstrap.php

@@ -23,7 +23,6 @@
  * @author     Tony Murray <murraytony@gmail.com>
  */
 
-use LibreNMS\Proc;
 use LibreNMS\Util\Snmpsim;
 
 global $config;