it turns out that the framework.TestContext.IPFamily variable is
not available for the DNS tests if they don't run in the initial
Ginkgo node when running in parallel.
We add a function to the framework to allow us to run command
only once per each Ginkgo node parallel execution.
It also adds a method to detect if the cluster is IPv6.
The use of the framework.TestContext.IPFamily variable guarantees
consistency all over the testing because this variable is only
assigned at the beginning of the testing.
