RFR: JDK-8241421 Cleanup handling of jtreg

Mon Mar 23 09:21:15 UTC 2020

We're doing some odd things in the build system for jtreg, most of it 
left-overs from the older build systems.

We have no need for JTREGEXE and it should be removed. We should also 
use the standard naming pattern of JTREG_HOME.

The test in BuildFailureHandler.gmk is a bit different -- it is supposed 
to fail. I have run it both with and without the patch, and verified 
that the test result and test log are basically the same, except for 
normal runtime variance like time stamps and certain randomness. I have 
also verified that testing through the Oracle CI system still works as 
expected.

Bug: https://bugs.openjdk.java.net/browse/JDK-8241421
WebRev: http://cr.openjdk.java.net/~ihse/JDK-8241421-cleanup-jtreg/webrev.01

/Magnus