Please approve fix for failing test JDK-8148638

[Martin Buchholz]

Sorry, I made a mistake in 8146467 and checked in a broken test.
Please approve my temporary fix
https://bugs.openjdk.java.net/browse/JDK-8148638
http://cr.openjdk.java.net/~martin/webrevs/openjdk9/CompletableFuture-temporary-revert/