Use @PYTHON@ directly instead of "#! /usr/bin/env"

Use @PYTHON@ directly instead of "#! /usr/bin/env"

In some installed python scripts /usr/bin/env is unnecessarily used in
shebang, replace it directly with @PYTHON@.

This will also avoid implicit dependency to /usr/bin/env in RPM distributions
and it will correctly add implicit dependency to /usr/bin/python instead.

Signed-off-by: Timothy Redaelli <tredaelli@redhat.com>
Signed-off-by: Joe Stringer <joe@ovn.org>