Test end-to-end with the real cluster (minikube)

[nolar]

Issue : #52

With this, the framework is tested for the very basic things, which can be missed in the unit-test: that it starts and works at all, and communicates with the Kubernetes API normally: both for watching and for patching.

Previously, we had an internal incident when the operator failed to start since the RBAC permissions were missing, but the unit-tests were all green. Now, such things should be detected.

The e2e tests are executed at the end, since they are usually slow (tens of seconds), and want the regular unit-tests to provide the results fast.

More e2e tests will be added in separate PRs. Currently, it is only a supporting infrastructure for this kind of tests, and a demo with the "./examples/" (also to check that the examples are still valid).

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Kubernetes 1.11.x is disabled since Minikube/kubeadm fails on the CRI preflight checks, and neither Kubernetes nor Minikube are our system-under-test — the framework and its examples are the the system-under-test.

Kubernetes 1.10.x is disabled due to conflicting behaviour of spec.version in CRD files: either 1.10 or 1.14 fails, but 1.14 is valuable as the future release, so 1.10 can be sacrificed (to not introduce the legacy on the project start).

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This is how it looks in Travis (as an example): https://travis-ci.org/nolar/kopf/builds/527762283

[zincr]

🤖 zincr found 0 problems , 1 warning

ℹ️ Dependency Licensing
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Details on how to resolve are provided below

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Dependency Licensing

All dependencies specified in package manager files must be reviewed, banned dependency licenses will block the merge, all new dependencies introduced in this pull request will give a warning, but not block the merge

Please ensure that only dependencies with licenses compatible with the license of this project is included in the pull request.

• ℹ️ Could not process requirements.txt for new dependencies