How to update the gatk base docker

How to update the GATK base docker image:

1. choose a new version number for the base image and manually update the version in scripts/docker/gatkbase/build_docker_base.sh
2. build the gatkbase image using that script and upload it to the gatk-dev docker repo or gcr-gatk-snapshots
   • cd to scripts/docker/gatkbase
   • run ./build_docker_base.sh
   • docker tag broadinstitute/gatk-dev:your-version-rc1 or whatever the correct tag is for where you want it uploaded
   • docker push tagname
3. update the Dockerfile in the main gatk to use the image you pushed
4. commit the changes to the two docker files and to a new pull request
5. wait for the tests to pass and show it to a reviewer
6. push the base image to the official gatk repo with the right name
7. update the main docker to point to the official version you just released
8. wait for tests to pass in travis and merge