update dcos gob example

[siggy]

The examples configs and instructions at https://github.com/BuoyantIO/linkerd-examples/tree/master/gob/dcos need updating.

1. Remove references to DC/OS linkerd and namerd universe package, use generic marathon configs instead.
2. Replace S3 config hosting with in-line configs piped to linkerd executables.
3. Consider sharing configs with https://github.com/BuoyantIO/linkerd-examples/tree/master/dcos/namerd-linkerd