ISPN-4677 Map/Reduce job fails with the wrong explanation on TimeoutException

Master only. See https://issues.jboss.org/browse/ISPN-4677 for discussion and rationale. 
Because Sanne suggested that we be more descriptive about the exception cause. It however turned out that we have more than one reason why this call may timeout with TimeoutException. So it is incorrect to claim that the "call did not complete within " certain timeout. That is why the wording is a bit more generic. I really think we should not spend more time on this "trivial" issue :-)