This addresses users issues in being unable to use RKE command line
using SSH_AUTH_SOCK. On OSX the socket env var is set, but nothing
is listening. Also, Linux users have reported issues. To address this
the default mode is to not use SSH Agent Auth. A user must set it
explicitly in either the config file or on the CLI. The only way
to use a passphrase protected key file is with a properly configured
SSH Agent and using SSH Agent Auth.
This defaults to using the SSH Agent or a passwordless key file.
It also refactors the Dialer methods a bit to simplify and decouple
the host object from the dialer.
Use separate cluster package
Save cluster state and certs to kubernetes
Handle Remove and sync cluster state/crts
Reuse kubernetes client and combine image and version
Separate building functions and small fixes
