Disable sshd GSSAPI auth

GSSAPI is not currently implemented in Fuel, so
it only slows incoming SSH connections. Disabling
it will enhance user experience.

Change-Id: I935e7c383e24663296c938e32b12682086d6797b
Closes-Bug: #1327988
Merge "Disable sshd GSSAPI auth" into stable/5.0