tools: improve git-version-next to always output version variables

tools: improve git-version-next to always output version variables

- Always output UL_NEXT_FINAL_RELEASE (previously only for RC releases)
- Add UL_LAST_FINAL_RELEASE for last stable (non-RC) release
- Remove _RAW variables from output for cleaner interface

The UL_NEXT_FINAL_RELEASE now represents the version that will be
released after code stabilization, while UL_LAST_FINAL_RELEASE
represents the last stable release without -rc suffix.

Signed-off-by: Karel Zak <kzak@redhat.com>