Adding regression tests.

* Coverage for datastore.
Simplified test for multiple entities
Merge pull request #33 from silvolu/master

Adding regression tests.
Create Error object for errors returned in the response body.
Fixed flaky test for Datastore.getAll().

* Order in returned objects is coherent with returned keys, but not necessarily with the keys passed as input.
Added custom error class for api errors
Merge pull request #36 from silvolu/master

Return Error object for failed Api requests and fixed flaky test.
Merge branch 'master' of github.com:GoogleCloudPlatform/gcloud-nodejs into eventemitter-subs
Include regression tests to coverage.
pubsub: Adding subscription creation.
pubsub: Fixing undefined callback.
pubsub: Add regression tests.