Optimize yamllint to run in one process (#15335)
Optimize yamllint to run in one process (#15335)

Previously we ran a new process for every yaml file. yamllint can just
take in a list of files to run, and handles this much more efficiently.
On my machine, this broguht runtime from 75s to 15s.
istio/istio,geeknoid/istio,smawson/istio,smawson/istio,geeknoid/istio,istio/istio,istio/istio,istio/istio,geeknoid/istio,geeknoid/istio,istio/istio,geeknoid/istio,smawson/istio,geeknoid/istio,smawson/istio,smawson/istio,smawson/istio