ceph: renew auth tickets before they expire

We were only requesting renewal after our tickets expire; do so before
that.  Most of the low-level logic for this was already there; just use
it.

Signed-off-by: Sage Weil <sage@newdream.net>

diff --cc fs/ceph/auth.c
Simple merge

diff --cc fs/ceph/auth.h
Simple merge

diff --cc fs/ceph/auth_none.c
Simple merge

diff --cc fs/ceph/auth_x.c
Simple merge