lualoader: Improve module loading diagnostics

[kevans]

Summary

Some fixes:

• Maintain historical behavior more accurately w.r.t verbose_loading; verbose_loading strictly prints "${module_name...}" and later "failed!" or "ok" based on load success
• With or without verbose_loading, dump command_errbuf on load failure. This usually happens prior to ok/failed if we're verbose_loading

[kevans]

Don't brick boots without the updated liblua... most commonly occurring if loader.efi's been installed to ESP, additional intervention is required.