if running under docker, read redis uri from env var
if running under docker, read redis uri from env var

expecting it to be passed as:

  sudo docker run -i -t -e CONFIG_REDIS_URI=`cat /s/etc/kato/redis_uri` stackato/appmdns

(does not affect tech preview)
(cherry picked from commit 64bb46d114602139ee16e8fe36277bab54ea2c1c)

hpcloud/stackato-go,ActiveState/stackato-go