Warning when starting Gerrit JVM without OOM protection

When gerrit.sh gets started from a non-root user, the JVM PID is not
protected against the Kernel OOM killer attacks.
Instead of silently ignoring the setting, display a warning making aware
of the danger and telling the user what to do.

Bug: Issue 9514
Change-Id: I4c1c0e06b260e75d900f436d37f0b91d031cd24e

gerrit-pgm/src/main/resources/com/google/gerrit/pgm/init/gerrit.sh

@@ -439,6 +439,11 @@ case "$ACTION" in
                 echo -16 > "/proc/${PID}/oom_adj"
             fi
         fi
+    elif [ "$(uname -s)"=="Linux" ] && test -d "/proc/${PID}"; then
+        echo "WARNING: Could not adjust Gerrit's process for the kernel's out-of-memory killer,"
+        echo "         one of the possible causes are ${0} not run as root."
+        echo "         Consider changing the OOM score adjustment manually for Gerrit's PID=${PID} with e.g.:"
+        echo "         echo '-1000' | sudo tee /proc/${PID}/oom_score_adj"
     fi
 
     TIMEOUT="$GERRIT_STARTUP_TIMEOUT"