Tests that nfd master-worker communication works and that the worker is
able to label the node with the labels from the 'fake' source.
An example of running the test suite with a custom image with user's
kubeconfig:
$ go test ./test/e2e/ -args -nfd.repo=<image-repo> -nfd.tag=<image-tag> \
-kubeconfig=$HOME/.kube/config
Partly based on some previous work done by Balaji Subramaniam.
Patch the (Kubernetes) e2e wireframe introduced in the previous commit with some minor
modifications, dropping some bits in order to simplify the code.
Also adds a dummy test stub for node feature discovery.
Also, adds new method WaitForReady() into NfdMaster.
In practice, this quite widely tests nfd-master, too, as the tests
create an instance of NfdMaster and verify that the communication
between master and worker works.
