Consider reading `LUA_PATH` and `LUA_CPATH`

[edubart]

Context

As discussed in our channel, we need to change ${LUA_PATH_5_4:-;} to ${LUA_PATH_5_4:-${LUA_PATH:-;}} so this work better with standard luarocks distros.

This change will also need to be made with our lua templates in tools/template.

Originally posted by @edubart in #171 (comment)