When creating a client read the GroupVersion value passed in the
restclient.Config. If the passed GroupVersion does not match current
group or is not enabled fallback to default GroupVersion for that group.
Previously, we would initialize the experimental client at factory creation
time. This is problematic because the clientConfig loader has values populated
from the command-line flag parsing, and these are not populated until after
Factory creation. Introduce an ExperimentalClientCache to create (and reuse)
ExperimentalClients.
Started looking at refactoring of the kubectl Factory, which
caused me to experience all 5 stages of grief. There are some options
for improving, but it probably warrants a proposal with some discussion/
feedback. In the meantime this tests `NegotiateVersion` in isolation.
