RFR(xs) 8231529: [TESTBUG] runtime/cds/appcds/dynamicArchive/DynamicLotsOfClasses.java shouldn't wrap SkippedException into Exception

[Calvin Cheung]

bug: https://bugs.openjdk.java.net/browse/JDK-8231529

webrev: http://cr.openjdk.java.net/~ccheung/8231529/webrev.00/

The fix is just simply removing the try-catch in the test. Two methods 
in TestCommon.java have been changed to throw Exception instead of 
Throwable.

Tested manually by modifying FileMap::map_region() to simulate a mapping 
failure.

Also ran tier1 - 3 tests successfully.

thanks,

Calvin