RFR(XXS): UnlockDiagnosticVMOptions flag is needed for ShenandoahVerify

[Zhengyu Gu]

Added UnlockDiagnosticVMOptions flag for HeapCommit test when 
ShenandoahVerify flag is specified.

Webrev: 
http://cr.openjdk.java.net/~zgu/shenandoah/missing_diag_flag/webrev.00/

Thanks,

-Zhengyu