Implementing remaining datastore regression tests from gcloud-node.
Uses pre-built wheels when pip installing from tox.

In addition:
- Creates script scripts/update_wheels_project.sh to kick off a new
  build when merging to master (outside of a PR).
- Moves update_docs into a larger group of merge scripts
  that happen when merging to master.
Merge pull request #307 from dhermes/finish-datastore-regression

Implementing remaining datastore regression tests from gcloud-node.
Merge pull request #308 from dhermes/speed-up-build-stage-two

Uses pre-built wheels when pip installing from tox.