Integration tests should fail rather than skip if project id is not set in Travis

[parthea]

Certain integration tests are skipped if a BigQuery project is not set in Travis. My initial thought is that the tests should fail if a BigQuery project id is not provided.

For reference, here are the steps to run the BigQuery integration tests on Travis:
https://pandas-gbq.readthedocs.io/en/latest/contributing.html#running-google-bigquery-integration-tests

[max-sixty]

This was merged to master earlier this year, closing