RFR(xs): 8204095: [TESTBUG] TestPrintReferences.java fails if multiple concurrent mark happens

[sangheon.kim at oracle.com]

Hi all,

Can I have reviews for this tiny patch?

TestPrintReferences.java compares total time of a phase and sum of 
sub-phases.
However it doesn't split values in different GCs so it could read total 
time from one GC and sum of sub-phases from followed GC.
This patch excludes other GCs from the first one so we are not affected 
by following GC values.

CR: https://bugs.openjdk.java.net/browse/JDK-8204095
Webrev: http://cr.openjdk.java.net/~sangheki/8204095/webrev.0
Testing: hs-tier1 and local tests.

Thanks,
Sangheon