The bin/jtreg.sh script currently uses JT_HOME and JT_JAVA to allow the use to specify where jtreg is installed and which copy of Java to run it.

A better convention would be to use JTREG_HOME and JTREG_JAVA, while retaining the old names to provide defaults if needed.

There are other minor typos to be cleaned up, and the script should also check for the use of JDK 8.