stand: lua: module names should permit more

The module entries should generally allow whatever is allowed as an
env_var in the pattern table. Notably, we're missing periods which
would allow proper entries for .dtb files in loader.conf that don't need
to specify a module_name entry for it.

%d in this expression is actually redundant as %w is actually
"all alphanumerics," but I've included it for now to match the env_var
entry. We should really remove it from both.

Reported by: "aribi" on the forums via allanjude@
MFC after: 1 week