[System.ServiceModel] Fix flaky Bug652331_2 test

[System.ServiceModel] Fix flaky Bug652331_2 test

The test sometimes failed on Jenkins with the timeout assert. Running only this single test locally
with `make check TESTNAME=System.ServiceModel.Dispatcher.Bug652331Test.Bug652331_2` however reproduced
this almost every single time.

It seems that WCF takes a bit to initialize until it accepts connections, so putting a little sleep
fixed this for me locally and running it in a loop for half an hour didn't assert even once.