Migrate python tasks to new-style options.

Testing Done:
CI passed.

Manually verified that flags work as expected, especially the global --interpreter flag, as used by these tasks.

Reviewed at https://rbcommons.com/s/twitter/r/1244/
Sync of https://github.com/pantsbuild/pants/commit/c7ba9278e1e9647d6ac764d72cfa1269e58093d5