RFR(XS): JDK-8150647 - Quarantine TestPLABResize.java until JDK-8150183 is fixed

[Jesper Wilhelmsson]

Hi,

In order to push hs-rt to main today we need to quarantine two tests that are 
broken.

JDK-8150647 - Quarantine TestPLABResize.java until JDK-8150183 is fixed
https://bugs.openjdk.java.net/browse/JDK-8150647

JDK-8150318 - serviceability/dcmd/jvmti/LoadAgentDcmdTest.java - Could not find 
JDK_DIR/lib/x86_64/libinstrument.so
https://bugs.openjdk.java.net/browse/JDK-8150318

I'm quarantining these in my local snapshot before pushing to main. In effect it 
will be the same thing as pushing hs-rt to main first and then push this change 
directly to main.

Webrev: http://cr.openjdk.java.net/~jwilhelm/8150183/webrev.00/

(A single change with two bug IDs. HG updater will close both quarantine bugs.)

Thanks,
/Jesper