The dynamic client will be needed to interact with any custom resource
that airshipctl doesn't know about. It will be required for checking the
health of a cluster, as well as any other operations that may need to be
performed on generic objects.
This also adds the pkg/k8s/client/fake package, which can be used to
create a mock instance of a client for use in unit tests.
Change-Id: Ia331ff4875a067045f6f9245daee109126fb1d33
Relates-To: #73
Relates-To: #20
ea9fba7278