re-install ginkgo script for switching between mac and linux
re-install ginkgo script for switching between mac and linux

Signed-off-by: Craig Furman <82b4b6d2372fcea863d8fd21c02d40060d303650@pivotal.io>

cloudfoundry-incubator/garden-linux,cloudfoundry-incubator/garden-linux,cloudfoundry-incubator/garden-linux