WIP - working on cloud storage import
Add import_data_from_uris and wait_for_job

The import_data_from_uris method imports data from Google Cloud
Storage.   The wait_for_job method takes a job resource or jobId
and waits until the job completes, polling with a user-specified interval
and timing out after a different user-specified interval.
Add wait_for_job test

Ensure that wait_for_job accepts a jobId.
Merge branch 'master' into cloudStorage
Test return type from BigQueryClient.wait_for_job is a dict
Merge branch 'master' into cloudStorage
Fix source_format constants used by import_data_from_uris
Fix bug: BigQuery load jobs now work

Got rid of the default values in import_data_from_uri.  If values are not
provided, they are not inserted into the load configuration.  Also fixed
the structure of the load configuration JSON.  Still need to write tests.