Silence verbose output when VERBOSE environment variable is not set

[yqxk]

Hello,

I sometimes run appimages in docker containers, which do not allow mounting of filesystems by default, so I run them with

APPIMAGE_EXTRACT_AND_RUN=1 NO_CLEANUP=1 <path to appimage>

After the first execution, subsequent runs produce many lines of "File exists and file size matches, skipping". It would be nice if we could silence these informational messages (redirecting stderr to /dev/null is not ideal as this also redirects error messages from the bundled app).

This string is output here, and the function this lives in already has access to a verbosity flag here; so it looks reasonably straightforward to implement it. Would this be possible?

Thanks for your work on this!

[TheAssassin]

PRs welcome refactoring the logging.