liblua: adds bufferlist and msgpack libraries

Adds basic Lua wrappers around ceph::bufferlist, the cmsgpack Lua
library, and builds Lua as a noinst shared library.

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>
cls_lua: add Lua object class

Adds cls_lua and associated tests. Supports many of the cls_cxx_*
functions. See test/cls_lua/ for examples.

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>
lua: support cls_cxx_write and bufferlist::length

Signed-off-by: Adam Manzanares <nmtadam@gmail.com>
Reviewed-by: Noah Watkins <noahwatkins@gmail.com>