py2/3: remove usage of long built-in
py2/3: remove usage of long built-in

We have six in requirements, there should be no issue with imports (six
is used natively in other parts of code too)

Signed-off-by: Martin Bašti <388356a3851efe39ff0604de6d8fb2e16e10a0b7@redhat.com>

fr34k8/atomic-reactor,DBuildService/atomic-reactor,projectatomic/atomic-reactor,DBuildService/atomic-reactor,fr34k8/atomic-reactor,projectatomic/atomic-reactor