For historical reasons InitConfiguration is used almost everywhere in kubeadm
as a carrier of various configuration components such as ClusterConfiguration,
local API server endpoint, node registration settings, etc.

Since v1alpha2, InitConfiguration is meant to be used solely as a way to supply
the kubeadm init configuration from a config file. Its usage outside of this
context is caused by technical dept, it's clunky and requires hacks to fetch a
working InitConfiguration from the cluster (as it's not stored in the config
map in its entirety).

This change is a small step towards removing all unnecessary usages of
InitConfiguration. It reduces its usage by replacing it in some places with
some of the following:

- ClusterConfiguration only.
- APIEndpoint (as local API server endpoint).
- NodeRegistrationOptions only.
- Some combinations of the above types, or if single fields from them are used,
  only those field.
Signed-off-by: Rostislav M. Georgiev <rostislavg@vmware.com>