Add EXTRA testing to CMake build

[edwardhartnett]

We test with sample files downloaded from the FTP site.

But I don't have permission to write files to the NOAA FTP site, so there's a long wait between when I develop a test with a new sample file, and the time I can start using that test in CI.

So the EXTRA option allows me to run tests on my machine (where the file exists already) until the file gets uploaded to the FTP site.

Once the file is available on the FTP site, the test will migrate out of EXTRA testing. So the current EXTRA tests are tests for which the test file is not yet uploaded to the FTP site.