Dockerfile.gerrit: Upgrade to Gerrit 3.7.6 and use LFS plugin

We're currently using 3.7.6 in production.

Install the lfs plugin too. A future commit will establish configuration for it.

Manual steps are required for upgrading Gerrit:

• Delete the javaHome setting from the [container] section in gerrit.config in the exp_train-dev-gerrit-etc Docker volume (/etc/gerrit/gerrit.config from inside to gerrit service container). This is most easily done before performing the rebuild, while the old Gerrit container is still running:

./train-dev docker-compose exec gerrit bash
bash-4.4$ vi /etc/gerrit/gerrit.config

• Start the rebuild:

./train-dev build <workspace-dir>

The operation will eventually fail like so:

waiting for gerrit to come online...
Error: No such container:

• Add the following to the gerrit service in exp/docker-compose.yml:

restart: "no"
entrypoint: [bash, -c, "java -jar /var/gerrit/bin/gerrit.war init -d /var/gerrit && java -jar /var/gerrit/bin/gerrit.war reindex -d /var/gerrit --index changes"]

• Restart the gerrit service to make it run the upgrade commands from the prior step:

./train-dev docker-compose up gerrit

This will show the progress of the upgrade and will eventually terminate.

• Remove the two lines added to exp/docker-compose.yml

• Restart the build, which should run to completion:

./train-dev build <workspace-dir>