Add Test runs for Python 3.7 and remove 3.4 (#5295)
Add Test runs for Python 3.7 and remove 3.4 (#5295)

* remove 3.4 from unit test runs

* add 3.7 to most packages. PubSub, Monitoring, BigQuery not enabled

* Fix #5292 by draining queue in a way compatible with SimpleQueue and Queue

googleapis/python-websecurityscanner,googleapis/python-websecurityscanner