Add e2e tests

[MarcelMue]

This is mainly for cases where unit tests with a fake k8s client don't work properly. Description by @fgimenez :

Also not related to this PR, could it be possible to add some e2e tests here? For reference, with these in place, we could install the endpoint-operator-chart built from the branch and test it on a k8s cluster, either with out-of-cluster (for example https://github.com/giantswarm/aws-operator/blob/master/e2e/project.yaml#L33) or in-cluster tests (like https://github.com/giantswarm/aws-operator/blob/master/e2e/tests/awstpr.go#L34). Let me know if I can be of any help with that.

[fgimenez]

It would involve these:

• Create circleCI 2.0 setup, like this one https://github.com/giantswarm/aws-operator/blob/master/.circleci/config.yml.
• Create an e2e directory like this one https://github.com/giantswarm/aws-operator/tree/master/e2e (once this lands https://github.com/giantswarm/e2e-harness/pull/7 it should be done with the e2e-harness cli tool). You should modify project.yaml https://github.com/giantswarm/aws-operator/blob/master/e2e/project.yaml, especially the installation of tthe endpoint-operator chart, looks like in values you should only need DockerConfigJSON https://github.com/giantswarm/aws-operator/blob/master/e2e/project.yaml#L29
• Change the project name in the Dockerfile
• Write your tests, they can be out of cluster (directly in the project.yaml file, like in https://github.com/giantswarm/e2e-harness/blob/master/e2e/project.yaml#L8, the setup and outOfCluster steps are the same) or in cluster (go tests like https://github.com/giantswarm/aws-operator/blob/master/e2e/tests/awstpr.go#L31).

I can propose a PR with a basic skeleton so that you can begin writing tests, let me know if I can help with that.

[MarcelMue]

I will hopefully get to this next week, I'll try to set up as you described above then. I'd suggest you don't invest time on this right now as it's not urgent yet.