ui: from new cluster GuideMe form adding host by pk fails

Adding host by public key failed on "cannot add host with empty
password" because the authentication method was not set properly to the
Add host request.

Change-Id: I7001e0766d52ac92fe17d6e84fbc42767007e5eb
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1057575
Signed-off-by: Yaniv Bronhaim <ybronhei@redhat.com>