ISPN-3312 & ISPN-3314

ISPN-3312 DistributedExecutionCompletionTest.testBasicTakeInvocationWithSleepingCallable random failures
ISPN-3314 DistributedTaskPart.isDone() doesn't return true unless get() was called before

https://issues.jboss.org/browse/ISPN-3312
https://issues.jboss.org/browse/ISPN-3314