refactor e2e mixer tests (#4678)
refactor e2e mixer tests (#4678)

based on https://github.com/istio/istio/pull/4185
istio/istio,smawson/istio,geeknoid/istio,frankbu/istio,frankbu/istio,geeknoid/istio,istio/istio,geeknoid/istio,smawson/istio,smawson/istio,geeknoid/istio,geeknoid/istio,frankbu/istio,frankbu/istio,geeknoid/istio,smawson/istio,smawson/istio,frankbu/istio,smawson/istio,istio/istio,frankbu/istio,istio/istio,istio/istio