Cache CLI parser objects (#11957)
Cache CLI parser objects (#11957)

Right now, when we are using the CLI parser in LocalTaskJob and
executor, having to re-create the parser each time adds a noticeable
overhead for quick tasks -- by caching this we save 0.07s

(I know that doesn't sound like much, but for an `echo true`
BashOperator task that takes it from 0.25s to 0.19s - i.e. it cuts the
time down by about 20%!)
mrkm4ntr/incubator-airflow,apache/incubator-airflow,danielvdende/incubator-airflow,DinoCow/airflow,nathanielvarona/airflow,nathanielvarona/airflow,airbnb/airflow,DinoCow/airflow,bolkedebruin/airflow,danielvdende/incubator-airflow,cfei18/incubator-airflow,mrkm4ntr/incubator-airflow,apache/incubator-airflow,mrkm4ntr/incubator-airflow,bolkedebruin/airflow,airbnb/airflow,nathanielvarona/airflow,mistercrunch/airflow,nathanielvarona/airflow,dhuang/incubator-airflow,sekikn/incubator-airflow,danielvdende/incubator-airflow,cfei18/incubator-airflow,mrkm4ntr/incubator-airflow,cfei18/incubator-airflow,apache/airflow,cfei18/incubator-airflow,Acehaidrey/incubator-airflow,Acehaidrey/incubator-airflow,sekikn/incubator-airflow,mistercrunch/airflow,apache/airflow,lyft/incubator-airflow,apache/incubator-airflow,cfei18/incubator-airflow,lyft/incubator-airflow,Acehaidrey/incubator-airflow,nathanielvarona/airflow,airbnb/airflow,Acehaidrey/incubator-airflow,danielvdende/incubator-airflow,dhuang/incubator-airflow,bolkedebruin/airflow,apache/airflow,apache/airflow,Acehaidrey/incubator-airflow,sekikn/incubator-airflow,apache/airflow,DinoCow/airflow,airbnb/airflow,lyft/incubator-airflow,Acehaidrey/incubator-airflow,nathanielvarona/airflow,bolkedebruin/airflow,lyft/incubator-airflow,DinoCow/airflow,danielvdende/incubator-airflow,bolkedebruin/airflow,sekikn/incubator-airflow,apache/incubator-airflow,cfei18/incubator-airflow,dhuang/incubator-airflow,apache/airflow,danielvdende/incubator-airflow,mistercrunch/airflow,dhuang/incubator-airflow,mistercrunch/airflow