8055111: [TESTBUG] jdk.testlibrary.Utils.removeGcOpts doesn't remove -Xconcgc

[Stefan Karlsson]

Hi all,

Please, review this patch to add -Xconcgc to the set of flags to be 
filtered out by Utils.removeGcOpts:
http://cr.openjdk.java.net/~stefank/8055111/webrev.00/

This fixes one of the instances in:
https://bugs.openjdk.java.net/browse/JDK-8019361 - [TESTBUG] Conflicting 
collector combinations in option list for GC tests

Tested by running:
jtreg -vmoption:-Xconcgc -jdk:/localhome/java/jdk-9-ea-bin-b26/ 
test/java/lang/management/MemoryMXBean/ResetPeakMemoryUsage.java
jtreg -vmoption:-XX:+UseConcMarkSweepGC 
-jdk:/localhome/java/jdk-9-ea-bin-b26/ 
test/java/lang/management/MemoryMXBean/ResetPeakMemoryUsage.java

thanks,
StefanK