RFR(XS): 8141706: [TESTBUG] Update tests failing due to changed behavior

[gerard ziemski]

hi all,

Please review this trivial fix where we add -XX:+UnlockDiagnosticVMOptions as needed now that 
-XX:+IgnoreUnrecognizedVMOptions can not be used to implicitly unlock flags anymore:

bug id: https://bugs.openjdk.java.net/browse/JDK-8141706
webrev: http://cr.openjdk.java.net/~gziemski/8141706_rev0


cheers