recover gracefully without env vars

[jbayer]

when running on docker you have to specify env variables or grace doesn't launch well without complaining about the env missing in the logs.

docker run --rm -i -t -p 8080:8080 -e INSTANCE_INDEX=0 -e PORT=8080 cloudfoundry/lattice-app /lattice-app

would be good to assume port 8080 and have instance index default to "unknown" or "?" when the env vars are not set.

[davidwadden]

created https://www.pivotaltracker.com/story/show/90420532 to track this effort. we will work with our pm to prioritize this into our backlog.

[davidwadden]

closing issue -- #90420532 has been accepted

this was addressed with 08e31e6a9a580c330ddea48f9d57216aa0f3370c