Fix for autopkgtest failures with 7.3.1+1-1

This MR fixes: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1070740

The vendoring patch did not update the path to the jar files in autopkgtests and autopkgtest was ran in the chroot with extra packages installed, so the issue was not detected in time.

Changes:

• Update jar path to reference JTREG_HOME in autopkgtest.

Testing:

• Rebuilt chroots
• Ran autopkgtest oracular

autopkgtest [08:37:42]: test self-test: -----------------------]
autopkgtest [08:37:42]: test self-test:  - - - - - - - - - - results - - - - - - - - - -
self-test            PASS
autopkgtest [08:37:42]: @@@@@@@@@@@@@@@@@@@@ summary
self-test            PASS

sid

make: Leaving directory '/tmp/autopkgtest.nI01Rk/build.Ebl/real-tree/make'
autopkgtest [08:45:53]: test self-test: -----------------------]
autopkgtest [08:45:53]: test self-test:  - - - - - - - - - - results - - - - - - - - - -
self-test            PASS
autopkgtest [08:45:53]: @@@@@@@@@@@@@@@@@@@@ summary
self-test            PASS