[AIRFLOW-3246] Make hmsclient optional in airflow.hooks.hive_hooks (#4080)
[AIRFLOW-3246] Make hmsclient optional in airflow.hooks.hive_hooks (#4080)

Delay the import right up until it is needed, like how we do with the thrift imports.
DinoCow/airflow,Acehaidrey/incubator-airflow,mtagle/airflow,lyft/incubator-airflow,mistercrunch/airflow,apache/airflow,danielvdende/incubator-airflow,wileeam/airflow,r39132/airflow,r39132/airflow,dhuang/incubator-airflow,r39132/airflow,dhuang/incubator-airflow,Fokko/incubator-airflow,danielvdende/incubator-airflow,DinoCow/airflow,apache/airflow,airbnb/airflow,bolkedebruin/airflow,cfei18/incubator-airflow,sekikn/incubator-airflow,cfei18/incubator-airflow,spektom/incubator-airflow,Fokko/incubator-airflow,DinoCow/airflow,sekikn/incubator-airflow,artwr/airflow,mrkm4ntr/incubator-airflow,danielvdende/incubator-airflow,apache/airflow,nathanielvarona/airflow,cfei18/incubator-airflow,artwr/airflow,mrkm4ntr/incubator-airflow,danielvdende/incubator-airflow,wooga/airflow,nathanielvarona/airflow,wooga/airflow,artwr/airflow,airbnb/airflow,DinoCow/airflow,lyft/incubator-airflow,jgao54/airflow,apache/airflow,spektom/incubator-airflow,wileeam/airflow,Acehaidrey/incubator-airflow,danielvdende/incubator-airflow,fenglu-g/incubator-airflow,apache/incubator-airflow,danielvdende/incubator-airflow,mrkm4ntr/incubator-airflow,dhuang/incubator-airflow,wooga/airflow,jgao54/airflow,Acehaidrey/incubator-airflow,sekikn/incubator-airflow,fenglu-g/incubator-airflow,Fokko/incubator-airflow,sekikn/incubator-airflow,bolkedebruin/airflow,mistercrunch/airflow,Acehaidrey/incubator-airflow,nathanielvarona/airflow,nathanielvarona/airflow,Fokko/incubator-airflow,mtagle/airflow,lyft/incubator-airflow,adamhaney/airflow,wileeam/airflow,fenglu-g/incubator-airflow,mistercrunch/airflow,nathanielvarona/airflow,fenglu-g/incubator-airflow,bolkedebruin/airflow,cfei18/incubator-airflow,wileeam/airflow,dhuang/incubator-airflow,airbnb/airflow,mtagle/airflow,apache/airflow,spektom/incubator-airflow,Acehaidrey/incubator-airflow,apache/airflow,mrkm4ntr/incubator-airflow,bolkedebruin/airflow,jgao54/airflow,cfei18/incubator-airflow,adamhaney/airflow,wooga/airflow,adamhaney/airflow,adamhaney/airflow,artwr/airflow,bolkedebruin/airflow,apache/incubator-airflow,cfei18/incubator-airflow,Acehaidrey/incubator-airflow,mistercrunch/airflow,mtagle/airflow,nathanielvarona/airflow,jgao54/airflow,airbnb/airflow,r39132/airflow,apache/incubator-airflow,spektom/incubator-airflow,apache/incubator-airflow,lyft/incubator-airflow