API: Do not require root password for host operations

This allows using public key authentication, and set root_password as
deprecated field.

Change-Id: I506b844df10acfc17dcbce271755d37fdcdf0c7e
Signed-off-by: Yedidyah Bar David <didi@redhat.com>
Signed-off-by: Yaniv Bronhaim <ybronhei@redhat.com>