libceph: support for advisory locking on RADOS objects

This patch adds support for rados lock, unlock and break lock.

Based heavily on code by Mike Christie <michaelc@cs.wisc.edu>.

Signed-off-by: Douglas Fuller <dfuller@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Mike Christie <mchristi@redhat.com>
Reviewed-by: Alex Elder <elder@linaro.org>