support simple-proxy linkerd modes

[siggy]

Currently linkerd-viz requires a linker-to-linker configuration to display metrics: https://github.com/BuoyantIO/linkerd-examples/blob/master/dcos/linker-to-linker/linkerd-config.yml

Modify linkerd-viz to display metrics when in a simple-proxy configuration: https://github.com/BuoyantIO/linkerd-examples/blob/master/dcos/simple-proxy/linkerd-config.yml