Implement FS.ReadDirFs to properly determine type of context source

[DannyBrito]

What this PR does / why we need it:

The issue is that when trying to use a context source as a patch, it is currently treated as directory, so the file processed to a tar file, and when trying to apply the patch is not found under the sources as it is not handled.

This doesn't fix the context issue to be able to handle different for a file or directory.

These simple aims to allow context source to be used a patch.

I would appreciate so guidance/feedback on how to properly go about this issue.

Which issue(s) this PR fixes (optional, using fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when the PR gets merged): Fixes #

Special notes for your reviewer:

Fixes #188