Lua: Install modules with LuaRocks

Replace the manual building and installation of Lua modules with LuaRocks,
a management system for Lua modules.

Added the regular Lua executable to execute LuaRocks.
LuaRocks libraries and executables are excluded from the image, since it's only
needed in build time.

Signed-off-by: Or Cohen <orc@fewbytes.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
Lua: Add lua-stdlib to available Lua modules

Contains many useful utilities to be used in the CLI.

Signed-off-by: Or Cohen <orc@fewbytes.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>