JDK 9 RFR of JDK-8129759: Mark two tests from DistinctOpTest.java and SliceOpTest.java as serialization hostile

[Amy Lu]

Testcase testStable was newly introduced in JDK-8129120 in 
DistinctOpTest, this test should be marked as serialization-hostile. 
(such tests will ignored by by lambda serialization testing framework). 
testSkipLimitOpsWithNonSplittingSpliterator from SliceOpTest also need 
same change.

Please review and sponsor this change:

bug: https://bugs.openjdk.java.net/browse/JDK-8129759
webrev: http://cr.openjdk.java.net/~amlu/8129759/webrev.00/

Thanks,
Amy