Standardise shebangs

Some modules use `#!/usr/bin/python` while some already use `#!/usr/bin/env python`. When running ansible from a virtualenv, any `local_action`s will use the system Python when executing the scripts which hardcode `/usr/bin/python` as the path.

This commit should normalise them all to `/usr/bin/env python` and won't affect people who just use the system Python anyway.