Bug#409360: GSSAPIAuthentication should be disabled by default

I just ran into this issue when sshing to a server with GSSAPIAuthentication
enabled. Even though I am not using GSSAPI auth, Debian's default on the client
side added 15s to the login time. I agree with other folks that GSSAPI auth is
unusual and should be disabled by default since it may cause significant delays.

# With GSSAPIAuthentication on
$ time ssh -v foo hostname
<snip>
debug1: Next authentication method: gssapi-with-mic
debug1: No credentials were supplied, or the credentials were
unavailable or inaccessible
No Kerberos credentials available (default cache: FILE:/tmp/krb5cc_1000)
debug1: No credentials were supplied, or the credentials were
unavailable or inaccessible
No Kerberos credentials available (default cache: FILE:/tmp/krb5cc_1000)
<snip>
real    0m15.204s
user    0m0.010s
sys 0m0.011s

# With GSSAPIAuthentication off
$ time ssh -v foo hostname
real    0m0.195s
user    0m0.014s
sys     0m0.007s