Migrate `pants.engine.exp` to `pants.engine.v2`.
Review Request #3800 — Created May 1, 2016 and submitted — Latest diff uploaded
|benjyw, jsirois, peiyu, stuhood|
Motivated by and dependent on https://rbcommons.com/s/twitter/r/3798/ - these are split for easier reviewability but will land in lockstep.
- Migrate `pants.engine.exp` wholesale to `pants.engine.v2` for general usage.
- Migrate and fixup tests.