ceph: don't set WRITE_PENDING too early

prepare_write_connect() prepares a connect message, then sets
WRITE_PENDING on the connection.  Then *after* this, it calls
prepare_connect_authorizer(), which updates the content of the
connection buffer already queued for sending.  It's also possible it
will result in prepare_write_connect() returning -EAGAIN despite the
WRITE_PENDING big getting set.

Fix this by preparing the connect authorizer first, setting the
WRITE_PENDING bit only after that is done.

Partially addresses http://tracker.newdream.net/issues/2424

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Sage Weil <sage@inktank.com>