Update to iPXE version to 1.21.1

- Build additional artifacts - ISO, UEFI, etc.
- Set default timeout on shell to fallthrough on failures
- Add ping command (enabling patch renamed to be more generic)
- Update build container to Debian 11
- Add VERSION file

Change-Id: I9476c1d6446f6943dcd084384ba2ae3d96f71128
7 files changed