fixed ERRAI-470 - errai-cdi-stress-test is leaking a thread after undepl...

Hi Jonathan, I have created fix for https://issues.jboss.org/browse/ERRAI-470
which is track for BZ880962.
I did not have tested, but believe this could work out. Please check it out, when you have time test it or I will try to do so tomorrow, thx Pavel