libceph: support for lock.lock_info

Add an interface for the Ceph OSD lock.lock_info method and associated
data structures.

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

Signed-off-by: Douglas Fuller <dfuller@redhat.com>
[idryomov@gmail.com: refactor, misc fixes throughout]
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Mike Christie <mchristi@redhat.com>
Reviewed-by: Alex Elder <elder@linaro.org>