Add subpackages for each lua version with the right direct dependency of
lua-filesystem. This avoids surprises and is more robust than rely on
indirect install_if in lua-filesystem.

It fixes the dependency chain for aconf that has no direct dependency of
lua interpreter, but uses uwsgi-lua.

Fixes commit b106a06b (main/lua-penlight: modernize abuild, remove
subpkgs, add rock_manifest, 2018-04-16)