[AIRFLOW-XXX] Reduce log spam in tests (#5174)
[AIRFLOW-XXX] Reduce log spam in tests (#5174)

The change I introduced in #5158 caused this sensor test to keep poking
in a busy loop, resulting in about 4k lines to the logs like:

> INFO  [airflow.task.operators] Poking callable: <function PythonSensorTests.test_python_sensor_false.<locals>.<lambda> at 0x7f354b1d0c80>

The fix is to make sure that poke_interval is set to _something_ greater
than zero.
mtagle/airflow,cfei18/incubator-airflow,danielvdende/incubator-airflow,mrkm4ntr/incubator-airflow,lyft/incubator-airflow,airbnb/airflow,lyft/incubator-airflow,mistercrunch/airflow,spektom/incubator-airflow,mtagle/airflow,mistercrunch/airflow,mrkm4ntr/incubator-airflow,Acehaidrey/incubator-airflow,cfei18/incubator-airflow,r39132/airflow,Fokko/incubator-airflow,sekikn/incubator-airflow,mistercrunch/airflow,sekikn/incubator-airflow,DinoCow/airflow,nathanielvarona/airflow,apache/airflow,apache/incubator-airflow,mrkm4ntr/incubator-airflow,Fokko/incubator-airflow,dhuang/incubator-airflow,apache/airflow,nathanielvarona/airflow,bolkedebruin/airflow,apache/incubator-airflow,r39132/airflow,sekikn/incubator-airflow,danielvdende/incubator-airflow,airbnb/airflow,r39132/airflow,mtagle/airflow,spektom/incubator-airflow,wileeam/airflow,Fokko/incubator-airflow,apache/airflow,wooga/airflow,mtagle/airflow,nathanielvarona/airflow,wooga/airflow,cfei18/incubator-airflow,cfei18/incubator-airflow,r39132/airflow,Acehaidrey/incubator-airflow,cfei18/incubator-airflow,airbnb/airflow,nathanielvarona/airflow,Fokko/incubator-airflow,DinoCow/airflow,dhuang/incubator-airflow,mrkm4ntr/incubator-airflow,airbnb/airflow,lyft/incubator-airflow,apache/airflow,wileeam/airflow,danielvdende/incubator-airflow,spektom/incubator-airflow,apache/airflow,dhuang/incubator-airflow,nathanielvarona/airflow,wooga/airflow,danielvdende/incubator-airflow,danielvdende/incubator-airflow,bolkedebruin/airflow,wooga/airflow,Acehaidrey/incubator-airflow,spektom/incubator-airflow,Acehaidrey/incubator-airflow,bolkedebruin/airflow,nathanielvarona/airflow,bolkedebruin/airflow,lyft/incubator-airflow,Acehaidrey/incubator-airflow,bolkedebruin/airflow,wileeam/airflow,cfei18/incubator-airflow,mistercrunch/airflow,wileeam/airflow,DinoCow/airflow,apache/incubator-airflow,DinoCow/airflow,apache/incubator-airflow,apache/airflow,danielvdende/incubator-airflow,Acehaidrey/incubator-airflow,dhuang/incubator-airflow,sekikn/incubator-airflow