Use python2 as a default interpreter.

In accordance with PEP-394, python2 scripts should use `python2` as an interpreter. This ensures compatibility with setups that use python3 as a default, while retaining compatibility with distributions that still ship python2 as a default and comply with PEP-394.

I've tested these changes on ArchLinux, using python3 as a default (which is what Arch ships by default), and then again by setting python2 as a default. Nothing seems to have broken, and this works as-is with python3 set as a default (ie: it still uses python2).