[WFLY-333][BZ-1126287] add a test for the wait-time statistic

Adds a test for https://issues.jboss.org/browse/WFLY-333
Please use bigger numbers, e.g, >= 20, for things like this. In the normal case, a big number does no harm as termination happens within milliseconds. The legitimate failure case due to some problem in the code will be rare or never, so having to wait a while to learn it failed doesn't matter. In the random in between case of a long gc pause or something, a bigger number ensures we don't get spurious test failures.