lttng: Split --with-lttng and --with-babeltrace options

Signed-off-by: Adam Crume <adamcrume@gmail.com>
rbd-replay: Add unit test for Ser

Signed-off-by: Adam Crume <adamcrume@gmail.com>
rbd_replay: Add unit test for batch_unreachable_from

This requires a fair amount of code reorganization, since the types in
the function signature were previously not in a header file.

Signed-off-by: Adam Crume <adamcrume@gmail.com>