unit-tests-helper: download consul for linux
unit-tests-helper: download consul for linux

Co-authored-by: Utako Ueda <c5738b62d376b6008768780d19980e9b499f1bae@pivotal.io>

cloudfoundry-incubator/cf-routing-release,cloudfoundry-incubator/cf-routing-release,cloudfoundry-incubator/cf-routing-release