lualoader: Use cli_execute_unparsed for commands passed in via loader.conf

This applies to:

• exec
• [module]_before
• [module]_error
• [module]_after

Before this commit, these used loader.perform to execute them as a pure,
unsalted loader command. This means that they were not able to take
advantage of any Lua-salted loader commands, like boot and autoboot, or pure
Lua loader commands (functions attached to the 'cli' module).

They now have access to the full arsenal, just shy of being able to execute
arbitrary Lua.