RFR(xs): 8235563: [TESTBUG] appcds/CommandLineFlagComboNegative.java does not handle archive mapping failure

[Calvin Cheung]

bug: https://bugs.openjdk.java.net/browse/JDK-8235563

webrev: http://cr.openjdk.java.net/~ccheung/jdk15/8235563/webrev.00/

In order to handle archive mapping failure, use the assertAbnormalExit 
method of the CDSTestUtils.Result class which throws a SkippedException 
upon encountering an archive mapping failure.

The mapping failure was seen in JDK11u and should not happen in JDK14 
due to JDK-8231610 (Relocate the CDS archive if it cannot be mapped to 
the requested address). The intention is to integrate this fix into 
JDK15 and then backport to 11u.

The fix passed tier1 and tier2 tests.

thanks,

Calvin