Update to pants 0.0.23.

- Update build files for the new syntax, which no longer requires
  'pants(...)' around target names.
- Remove no-longer-supported "timeout" from python_tests.

Testing Done:
- Ran all unit tests: several fail, but they also fail under the previous version of pants.
- Built all python_binary targets in src/main/python/apache/aurora.
- Verified that resulting pexes executed correctly.

Bugs closed: aurora-695

Reviewed at https://reviews.apache.org/r/25543/