[AIRFLOW-4511] Fixes Travis CI stalling at pip install, docker pull (#5278)
[AIRFLOW-4511] Fixes Travis CI stalling at pip install, docker pull (#5278)


(cherry picked from commit 795f386f391b5b03ff1de0f846c14527d81334af)

owlabs/incubator-airflow,owlabs/incubator-airflow,owlabs/incubator-airflow,owlabs/incubator-airflow