[TOOLS] Add -e and --envfile flags to test.sh to pass environment (#2588)
[TOOLS] Add -e and --envfile flags to test.sh to pass environment (#2588)

* Add -e and --envfile flags to test.sh to pass environment

* It is sufficient to write the envvar to a file

* Also allow the docker image to be overridden

mesosphere/dcos-commons,mesosphere/dcos-commons,mesosphere/dcos-commons,mesosphere/dcos-commons,mesosphere/dcos-commons