RFR(XS) 8231367 [TESTBUG] ParallelLoadTest.java fails with "test.dynamic.dump not supported"

[Ioi Lam]

https://bugs.openjdk.java.net/browse/JDK-8231367
http://cr.openjdk.java.net/~iklam/jdk14/8231367-parallel-load-test-dynamic-dump.v01/

Mach5 testing tier-4 runs some of the CDS tests with 
-Dtest.dynamic.cds.archive=true.
This test fails because it has only one JAR file. When we put the JAR 
file on the boot
classpath, the app classpath becomes empty, which the 
"test.dynamic.cds.archive"
testing mode doesn't like.

The fix is to split the JAR file into two part, so we always have 
something in the app
classpath.

I also fixed the grammar in the error message TestCommon.java.

Thanks
- Ioi