Automatic merge from submit-queue

Node E2E: Make it possible to share test between e2e and node e2e

This PR is part of the plan to improve node e2e test coverage.
* Now to improve test coverage, we have to copy test from e2e to node e2e.
* When adding a new test, we have to decide its destiny at the very beginning - whether it is a node e2e or e2e.

This PR makes it possible to share test between e2e and node e2e. 
By leveraging the mechanism of ginkgo, as long as we can import the test package in the test suite, the corresponding `Describe` will be run to initialize the global variable `_`, and the test will be inserted into the test suite. (See https://github.com/onsi/composition-ginkgo-example)

In the future, we just need to use the framework to write the test, and put the test into `test/e2e/node`, then it will be automatically shared by the 2 test suites.

This PR:
1) Refactored the framework to make it automatically differentiate e2e and node e2e (Mainly refactored the `PodClient` and the apiserver client initialization).
2) Created a new directory `test/e2e/node` and make it shared by e2e and node e2e.
3) Moved `container_probe.go` into `test/e2e/node` to verify the change.

@kubernetes/sig-node 

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