There are times when previous actions have already extracted at least
some files to the cache location. This results in subsequent cache
extraction operations to emit errors such as:

> /usr/bin/tar: [dest_file_path]: Cannot open: File exists

This adds the --overwrite flag to the extract call to force tar to
just overwrite these files rather than reporting errors.

Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>