Run frontend localdb end2end tests in backend repo

[inodb]

Run the e2e localdb test in backend repo: https://github.com/cBioPortal/cbioportal-frontend/blob/master/.circleci/config.yml#L178. Currently in the frontend repo when you open a PR to the master branch, that frontend code is tested against a backend docker container running the latest master code. In the backend we would like the same thing but then testing the backend changes, that is:

1. build a docker image for this backend (or get a war in some other way)
2. find the frontend commit in pom.xml (https://github.com/cBioPortal/cbioportal/blob/master/pom.xml#L273)
3. check that out and run the localdb e2e tests against the image from 1. No need to spin up a frontend separately, since that's bundled in the war from 1.

A previous attempt was made here: https://github.com/cBioPortal/cbioportal/pull/4124/files#diff-1d37e48f9ceff6d8030570cd36286a61R20. This include downloading the jar from jitpack which is no longer necessary, since we have a Docker container now for the backend. The previous attempt stalled, since it proved tricky to get the tests to pass. The remote e2e tests expected quite a heavy machine, with the CircleCI backend machine the same set of e2e tests would result in failures. This should no longer be a problem with the localdb tests, since in the frontend all the containers are running on CirlceCI infrastructure.

More comprehensive documentation about running the localdb tests e2e can be found here: https://github.com/cBioPortal/cbioportal-frontend#run-of-local-e2e-tests