Trim cmake messages / avoid scaring users

[ChrisJChang]

We have had the suggestion to revisit our cmake messages to understand when our printing is actually informative vs confusing.

Some examples:

• The hdf5 and h5py incomaptibility is a bold red error, although as I understand it, it just ditches pbarlike. So it should really not seem like a significant error.
• Repeated messages about missing backends / scanners for different versions of the same backend / scanner. If it found a version, it should be a problem.
• A lot of successful cmake messages are printed to error stream
• "Werror is disabled" is printed in red, suggesting it might be a problem.