Sort the RSA host key before the DSA host key

The OpenSSH client appears to prefer the RSA host key if it is
available from the server when updating ~/.ssh/known_hosts, so
we should display that first if there are multiple keys, as it
is what the end-user would likely try to match the fingerprint
against when doing a visual key comparsion.

Signed-off-by: Shawn O. Pearce <sop@google.com>