[2.0.x] Faster disk find for LPC1768, Auto-build CDC support fix, error handling improvements

[Bob-the-Kuhn]

1. upload_extra_script.py is faster and only executes if doing an upload (if run under Auto-build)
2. CDC bootloader uploads now work. Turned out that AVRDUDE 5.10 could do the uploads but the newest version (6.3) can't. That means that we need to supply the correct version of AVRDUDE. Auto-build grabs the correct AVRDUDE image out of the Atom directory. Sometimes there's hangs at the end of the upload but the code is always there.
3. Added more error handling when trying to move the AT90USB JSON file to the PlatformIO directory. If Auto-build can't verify the JSON is in the proper location it'll warn the user that they'll have to manually move the file and then gives the full source & destination paths.
4. Added routine to calculate the percent FLASH & RAM used. This is only needed by the AT90USB boards when doing an upload. All the others situations already have this automatically done by PlatformIO. Sometimes this doesn't show up if the CDC upload hangs.
5. At90USB boards will now only look for the upload port when doing an upload.
6. Found another way a file path is presented during an error situation & added support for it.

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This PR implements the last of the major features I like to use when debugging problems.

TO DO

• Visual Studio support
• Documentation