lua: provide cls_lua_client library

Provides an interface that doesn't depend on Ceph encoding for users
outside of the Ceph source tree.

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>
test: use cls_lua client library for unit tests

...rather than using Ceph encoding directrly.

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>