Invoker agent failed to pull docker images if using docker registry name (#4488)
Invoker agent failed to pull docker images if using docker registry name (#4488)

Add `pip install docker` to Dockerfile for ow-utils to fix problem pulling docker images
sven-lange-last/openwhisk,RSulzmann/openwhisk,RSulzmann/openwhisk,markusthoemmes/openwhisk,rabbah/openwhisk,openwhisk/openwhisk,jeremiaswerner/openwhisk,houshengbo/openwhisk,akrabat/openwhisk,markusthoemmes/openwhisk,rabbah/openwhisk,markusthoemmes/openwhisk,houshengbo/openwhisk,rabbah/openwhisk,RSulzmann/openwhisk,markusthoemmes/openwhisk,RSulzmann/openwhisk,akrabat/openwhisk,openwhisk/openwhisk,jasonpet/openwhisk,style95/openwhisk,jasonpet/openwhisk,style95/openwhisk,houshengbo/openwhisk,jasonpet/openwhisk,style95/openwhisk,sven-lange-last/openwhisk,jeremiaswerner/openwhisk,jeremiaswerner/openwhisk,houshengbo/openwhisk,jeremiaswerner/openwhisk,akrabat/openwhisk,RSulzmann/openwhisk,jeremiaswerner/openwhisk,jeremiaswerner/openwhisk,jasonpet/openwhisk,style95/openwhisk,akrabat/openwhisk,houshengbo/openwhisk,houshengbo/openwhisk,sven-lange-last/openwhisk,markusthoemmes/openwhisk,RSulzmann/openwhisk,houshengbo/openwhisk,sven-lange-last/openwhisk,rabbah/openwhisk,openwhisk/openwhisk,rabbah/openwhisk,akrabat/openwhisk,markusthoemmes/openwhisk,RSulzmann/openwhisk,jasonpet/openwhisk,markusthoemmes/openwhisk,sven-lange-last/openwhisk,markusthoemmes/openwhisk,jasonpet/openwhisk,rabbah/openwhisk,openwhisk/openwhisk,sven-lange-last/openwhisk,style95/openwhisk,rabbah/openwhisk,akrabat/openwhisk,jasonpet/openwhisk,akrabat/openwhisk,style95/openwhisk,sven-lange-last/openwhisk,jeremiaswerner/openwhisk,openwhisk/openwhisk,style95/openwhisk,openwhisk/openwhisk