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@
Approved by: re (gjb)

(cherry picked from commit 5bc1e0c2285e73fe8455bb6c72b2b40e33f5477e)
(cherry picked from commit 6b2f0a3c31dbf9268b49d64c859da136ca8dc201)