RFR(xs) 8231097: [TESTBUG] runtime/cds/appcds/DirClasspathTest.java can fail with a mapping error

[Calvin Cheung]

bug: https://bugs.openjdk.java.net/browse/JDK-8231097

webrev: http://cr.openjdk.java.net/~ccheung/8231097/webrev.00/

Several CDS tests in tier-4 failed when running with 
-Dtest.dynamic.cds.archive=true due to mapping of the base archive has 
failed. The tests should be more tolerant on mapping failure by throwing 
a SkippedException.

The failures were observed on windows and are hard to reproduce. The 
change was tested by simulating the mapping failure in 
FileMapInfo::map_region by temporary adding the following code at the 
beginning:

if (1) {
     fail_continue("Unable to map ReadOnly shared space at required 
address");
     _memory_mapping_failed = true;
     return NULL;
}

Also ran mach5 tier4 tests.

thanks,

Calvin