Use local variations for python version splits

Use a local variation for python version splits.  This causes
dependencies from python modules not to look for variations
that match the version split, which will simplify a python module
depending on a java module (for example for test data) because
Soong won't look for a python version variant of the java module.

Bug: 173977903
Test: go test ./python
Change-Id: Ib034140c478ffbc7467ab830d3cfa5683c31d05c