bump vizzini
bump vizzini

Submodule src/code.cloudfoundry.org/vizzini 11092a4..856bd25:
  > Use IndexCounter helper in scale-down routing test

cloudfoundry-incubator/diego-release,cloudfoundry-incubator/diego-release,cloudfoundry-incubator/diego-release,cloudfoundry-incubator/diego-release