python: Fixup python shebangs to python3.

python: Fixup python shebangs to python3.

Builds on RHEL 8.2 systems are failing due to this issue.

See [1] as to why this is necessary.

I used the following command to identify files that need this fix:
find . -type f -executable | /usr/lib/rpm/redhat/brp-mangle-shebangs

I also updated the copyright notices as needed.

1. https://fedoraproject.org/wiki/Changes/Make_ambiguous_python_shebangs_error

Fixes: 1ca0323e7c29 ("Require Python 3 and remove support for Python 2.")
Signed-off-by: Greg Rose <gvrose8192@gmail.com>
Acked-by: Aaron Conole <aconole@redhat.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>