print/hplip and print/hplip-plugin: Fix URL and LICENSE information.

The URL change reflects a recent website change by HP, and was
preventing print/hplip-plugin from fetching correctly.

The LICENSE change reflects the fact that the introductory license
to the python source files mention that a later version of the GPL
can optionally be used.

PR: 224435
PR: 224408
Submitted by: Mason Loring Bliss <mason@blisses.org>
Reported by: jhb
Reviewed by: jhb
MFH: 2017Q4