python: add support for lockspace events

Add support for sending events to other hosts and listening for
lockspace events.

I added thin wrappers for sanlock_reg_event, sanlock_get_event,
sanlock_end_event, and sanlock_set_event.

Where sanlock C API has unused arguments, the Python bindings do not use
them, since we can add them later as optional arguments in a backward
compatible manner. This ensures that new code depending on this argument
will fail when working with a version that does not provide it.

sanlock_get_event returns one event per call. The Python version is
easier to use, returning list of events in one call, similar to
get_hosts.

Signed-off-by: Nir Soffer <nsoffer@redhat.com>