[8u60] approval request for JDK-8129532: LFMultiThreadCachingTest.java failed with ConcurrentModificationException

[Konstantin Shefov]

Please approve Test-only fix direct backport.

Exception is that "@key randomness" will be removed, because it is not 
supported in JDK 8u testbase.

bug: https://bugs.openjdk.java.net/browse/JDK-8129532
jdk9 review thread: 
http://mail.openjdk.java.net/pipermail/core-libs-dev/2015-June/034230.html
jdk9 changeset: http://hg.openjdk.java.net/jdk9/dev/jdk/rev/63bc43b5daa7

Thanks,
-Konstantin