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: NDouglas Fuller <dfuller@redhat.com>
[idryomov@gmail.com: refactor, misc fixes throughout]
Signed-off-by: NIlya Dryomov <idryomov@gmail.com>
Reviewed-by: NMike Christie <mchristi@redhat.com>
Reviewed-by: NAlex Elder <elder@linaro.org>