[Testbug] serviceability/dcmd/jvmti/*DcmdTest tests can't tolerate unrelated warnings

----------System.out:(66/3876)----------
[TestNG] Running:
  serviceability/dcmd/jvmti/DataDumpDcmdTest.java

Running DCMD 'JVMTI.data_dump' through 'PidJcmdExecutor'
Executing command '[/scratch/opt/mach5/mesos/work_dir/jib-master/install/2018-01-31-0554197.david.holmes.jdk-master/linux-x64-debug.jdk/jdk-11/fastdebug/bin/jcmd, 6278, JVMTI.data_dump]'
Command returned with exit code 0
---------------- stdout ----------------
6278:
Command executed successfully

---------------- stderr ----------------
Java HotSpot(TM) 64-Bit Server VM warning: Global variable for obsolete special flag entry "FastTLABRefill" should be removed
Java HotSpot(TM) 64-Bit Server VM warning: Global variable for obsolete special flag entry "SafepointSpinBeforeYield" should be removed
Java HotSpot(TM) 64-Bit Server VM warning: Global variable for obsolete special flag entry "DeferThrSuspendLoopCount" should be removed
Java HotSpot(TM) 64-Bit Server VM warning: Global variable for obsolete special flag entry "DeferPollingPageLoopCount" should be removed
Java HotSpot(TM) 64-Bit Server VM warning: Global variable for expired flag entry "UseCGroupMemoryLimitForHeap" should be removed

----------------------------------------

test DataDumpDcmdTest.cli(): failure
java.lang.RuntimeException: stderr was not empty
at jdk.test.lib.process.OutputAnalyzer.stderrShouldBeEmpty(OutputAnalyzer.java:96)
at DataDumpDcmdTest.run(DataDumpDcmdTest.java:48)


Similarly for LoadAgentDcmdTest.java