image analysis scratch space removal partially fails if image files have non-readable modes

[nurmi]

In rare cases, a condition has been observed where files inside an image's layer tarballs have a file mode that results in non-readable files when extracted (i.e. mode 0x0000). Some anchore analyzers extract targetted files for analysis, and when this occurs the extracted files cannot be removed from the analysis scratch space after image analysis is completed.

This condition doesn't prevent images from being analyzed, but it does create left over data in analysis scratch space that could grow slowly over time.

Proposed solution is to explicitly detect this condition and ensure that such files have a readable mode when temporarily extracted, so that they can be removed cleanly upon analysis completion.