This is a code cleanup and addition of an explanatory comment. For some
reason, the code related to the CLI guessing whether a path requires
sudo, has been interleaved into plugin_helpers.go, which was previously
purely code used on the server side in the implementation of Vault
plugins.
This remedies that by dividing the sudo paths code to a separate file,
and adds a comment to plugin_helpers.go providing future readers with
information about the overall theme of the file.
No code has been changed - only moved and documented.
