This has been a recurring ask and we had initially just made the change to
the cloud-init 2.0 codebase.  As the current thinking is we'll just
continue to enhance the current codebase, its desirable to relicense to
match what we'd intended as part of the 2.0 plan here.

- put a brief description of license in LICENSE file
- put full license versions in LICENSE-GPLv3 and LICENSE-Apache2.0
- simplify the per-file header to reference LICENSE
- tox: ignore H102 (Apache License Header check)

Add license header to files that ship.
Reformat headers, make sure everything has vi: at end of file.

Non-shipping files do not need the copyright header,
but at the moment tests/ have it.