Update & fix travis build/test process

[Eric Liu]

Our tests/build is failing on Travis for unknown reasons (e.g., import errors from scipy/numpy internals). My guess is due to dependency on out of date packages (or too new packages) or even old linux version.

We should get this back in a working state.

While we're here, the MOE build process on travis takes a ridiculously long time due to building numpy & scipy from scratch. I let this slide in the past and relied solely on local testing due to it being so slow... which kind of circumvents the point.

Some more things to do:

• build requirements.txt automatically from setup.py. this should be done by constructing a temporary virtualenv, installing moe, and freezing
  • this should be a "requirements" target in the makefile. depends on setup.py. test should depend on it.
• use wheels, pypi as much as possible. taking some 30min to build MOE is nuts
• consider venv-update and/or pip-faster: https://github.com/Yelp/venv-update (wont help with build times, but still handy for developers)
  • this makes virtualenvs a natural/automatic part of working with MOE (no more people skipping that step)