Remove notes about datetime.date objects and timezone matching.

Issues #278 and #279 have been filed to address.
Document regression tests, make run_regression fail if environ not set.
Adding support for queries in regression test.

This ports the gcloud-node regression tests for queries
over to gcloud-python.
Making tox regression handle all local and Travis simultaneously.
Making get_dataset() in regression utils use a global.
Merge pull request #281 from dhermes/functional-test-part2

Functional test - Add datastore query tests