[AIRFLOW-2959] Refine HTTPSensor doc (#3809)
[AIRFLOW-2959] Refine HTTPSensor doc (#3809)

HTTP Error code other than 404,
or Connection Refused, would fail the sensor
itself directly (no more poking).
cfei18/incubator-airflow,wileeam/airflow,malmiron/incubator-airflow,dhuang/incubator-airflow,nathanielvarona/airflow,mtagle/airflow,dhuang/incubator-airflow,apache/airflow,nathanielvarona/airflow,danielvdende/incubator-airflow,mrkm4ntr/incubator-airflow,akosel/incubator-airflow,sid88in/incubator-airflow,apache/incubator-airflow,apache/airflow,nathanielvarona/airflow,Fokko/incubator-airflow,mistercrunch/airflow,mrkm4ntr/incubator-airflow,Acehaidrey/incubator-airflow,apache/incubator-airflow,mtagle/airflow,sekikn/incubator-airflow,nathanielvarona/airflow,danielvdende/incubator-airflow,DinoCow/airflow,airbnb/airflow,lyft/incubator-airflow,r39132/airflow,sekikn/incubator-airflow,criccomini/airflow,adamhaney/airflow,wooga/airflow,spektom/incubator-airflow,Acehaidrey/incubator-airflow,sid88in/incubator-airflow,malmiron/incubator-airflow,criccomini/airflow,jgao54/airflow,malmiron/incubator-airflow,Acehaidrey/incubator-airflow,bolkedebruin/airflow,wileeam/airflow,artwr/airflow,lyft/incubator-airflow,lyft/incubator-airflow,bolkedebruin/airflow,danielvdende/incubator-airflow,jgao54/airflow,andyxhadji/incubator-airflow,Fokko/incubator-airflow,r39132/airflow,cfei18/incubator-airflow,Fokko/incubator-airflow,spektom/incubator-airflow,cfei18/incubator-airflow,fenglu-g/incubator-airflow,sekikn/incubator-airflow,r39132/airflow,andyxhadji/incubator-airflow,adamhaney/airflow,DinoCow/airflow,mistercrunch/airflow,wileeam/airflow,DinoCow/airflow,mistercrunch/airflow,Acehaidrey/incubator-airflow,lyft/incubator-airflow,andyxhadji/incubator-airflow,artwr/airflow,mistercrunch/airflow,akosel/incubator-airflow,cfei18/incubator-airflow,adamhaney/airflow,criccomini/airflow,airbnb/airflow,malmiron/incubator-airflow,Acehaidrey/incubator-airflow,apache/airflow,fenglu-g/incubator-airflow,DinoCow/airflow,wooga/airflow,bolkedebruin/airflow,airbnb/airflow,danielvdende/incubator-airflow,mrkm4ntr/incubator-airflow,sid88in/incubator-airflow,Acehaidrey/incubator-airflow,nathanielvarona/airflow,sid88in/incubator-airflow,apache/airflow,apache/airflow,apache/incubator-airflow,airbnb/airflow,spektom/incubator-airflow,akosel/incubator-airflow,jgao54/airflow,fenglu-g/incubator-airflow,dhuang/incubator-airflow,mrkm4ntr/incubator-airflow,artwr/airflow,cfei18/incubator-airflow,cfei18/incubator-airflow,bolkedebruin/airflow,mtagle/airflow,artwr/airflow,mtagle/airflow,nathanielvarona/airflow,wooga/airflow,apache/incubator-airflow,andyxhadji/incubator-airflow,criccomini/airflow,wooga/airflow,spektom/incubator-airflow,bolkedebruin/airflow,dhuang/incubator-airflow,fenglu-g/incubator-airflow,danielvdende/incubator-airflow,r39132/airflow,wileeam/airflow,sekikn/incubator-airflow,akosel/incubator-airflow,apache/airflow,adamhaney/airflow,Fokko/incubator-airflow,jgao54/airflow,danielvdende/incubator-airflow