doc/testing/end-to-end.md: add end-to-end.md doc (#408)

* doc/testing/end-to-end.md: add end-to-end.md doc

* doc/testing/end-to-end.md: suggestions from hasbro17

Author: AlexNPavel

doc/testing/end-to-end.md

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+# E2E Testing the Operator SDK
+The operator-sdk is automatically tested using both unit tests and e2e tests anytime
+a pull request is made. The e2e tests ensure that the operator-sdk acts as intended by
+simulating how a typical user might use the SDK. The automated tests test each PR and run in
+Travis CI, and Travis CI has a couple of features to simplify the e2e tests that we run.
+However, it is possible to run the e2e tests locally as well.
+
+## Running the E2E Tests Locally
+To run the tests locally, the tests either need access to a remote kubernetes cluster or a
+local minikube instance running on the machine.
+
+### Remote Kubernetes Instance
+To run the tests on a remote cluster, the tests need access to a remote kubernetes cluster
+running kubernetes 1.10 as well as a docker image repo to push the operator image to,
+such as quay.io. To run the test, use this command:
+```
+$ go test ./test/e2e/... -kubeconfig "path-to-config" -image "<repository>:<tag>"
+```
+
+This will run the tests on the cluster specified by the provided kubeconfig and the
+memcached-operator image that is built will be pushed to `<repository>:<tag>`.
+
+### Local Minikube Instance
+To run the e2e tests on a local minikube cluster, the minikube instance must be
+started and the host's docker client must be linked to the minikube instance's docker daemon,
+which allows the host to add images to the minikube's local image registry directly.
+To do this, run these commands:
+```
+$ minikube start --kubernetes-version v1.10.0
+$ eval $(minikube docker-env)
+```
+
+Once that is complete, the test can be run with this command:
+```
+$ go test ./test/e2e/...
+```
+
+The test will run using the kube config in $HOME/.kube/config (which is where the minikube
+kubeconfig is placed by default) and the operator image will be built and stored on the
+minikube instance's local image registry.
+
+## Cleanup of the E2E Tests
+The e2e tests create a new project using the operator-sdk to run in the provided
+cluster. The tests are designed to cleanup everything that gets created, but some errors
+can cause these cleanups to fail. For example, if a segfault occurs or a user kills the
+testing process, the cleanup functions will not run. To manually clean up a test:
+1. Delete the created project in $GOPATH/src/github.com/example-inc/memcached-operator
+2. Delete the namespaces that the tests run in, which also deletes any resources created
+within the namespaces. The namespaces start with `memcached-memcached-group`.
+3. Delete the CRD (`kubectl delete -f deploy/crd.yaml`).