RFR(XS): 8209534: [TESTBUG]runtime/appcds/cacheObject/ArchivedModuleCompareTest.java fails with EnableJVMCI

[Jiangli Zhou]

Please review the fix for the test bug in 
runtime/appcds/cacheObject/ArchivedModuleCompareTest.java.

ArchivedModuleCompareTest.java checks the archived system modules by 
comparing the boot layer modules from a -Xshare:off run and a -Xshare:on 
run. The -Xshare:off run in the test does not include the extra 
arguments from jtreg. Failure happens when running the test with 
"-XX:+UnlockExperimentalVMOptions -XX:+EnableJVMCI" (additional system 
modules are included in the boot layer with +EnableJVMCI). The fix is to 
use TestCommon.execOff() for the -Xshare:off process. Like 
TestCommon.exec(), TestCommon.execOff() handles the extra args from jtreg.

webrev: http://cr.openjdk.java.net/~jiangli/8209534/webrev.00/
bug: https://bugs.openjdk.java.net/browse/JDK-8209534?filter=14921

Tested ArchivedModuleCompareTest.java with 
"-XX:+UnlockExperimentalVMOptions -XX:+EnableJVMCI" locally. Also ran 
tier1, tier2 and tier3 via mach5.

Thanks,

Jiangli