cls_lua: don't use Ceph message encoding

Switches away from Ceph type encoding to MsgPack so that the lua-rados
wrapper library can interact with cls_lua without relying on any
installed cls_lua_client libraries. This is because Ceph type encoding
isn't publically exposed (yet..).

This also removes the message log contained in the reply structure.

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

Sandboxing has been removed for the time being. A way to properly
configure this is needed. For instance, g_conf->cls_lua_use_sandbox
would be useful, but some effort to figure out all the parameters to the
Lua VM setup is needed before settling on something permanent.

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