The debian openjdk-11-jre-headless package lacks tools like jcmd which
can be useful for debugging the jvm and applications running on top of
the jvm. In particular I had to use `kill -3 $JVM_PID` to get a thread
dump (which worked) instead of jcmd during a recent Gerrit outage.
Since you don't know that you'll need these tools until its too late go
ahead and switch to the jdk package instead of the jre package to be
prepared in the future.
Change-Id: I09a81f1abc6e528b4ffd624050698a99c264f499
95c7264ee9