For file discovery, in case the user feeds a file for the CA
from the kubeconfig, make sure it's preloaded and embedded using
the new function EnsureCertificateAuthorityIsEmbedded().
This commit also applies cleanup:
- unroll validateKubeConfig() into ValidateConfigInfo() as this way
the default cluster can be re-used.
- in ValidateConfigInfo() reuse the variable config instead of creating
a new variable kubeconfig.
- make the Ensure* functions return descriptive errors instead of
wrapping the errors on the side of the callers.
- move most unrelated to phases output to klog.V(1)
- rename some prefixes for consistency - e.g.
[kubelet] -> [kubelet-start]
- control-plane-prepare: print details for each generated CP
component manifest.
- uppercase the info text for all "[reset].." lines
- modify the text for one line in reset
