Using a vanilla Grafana Docker image as part of `conduit install`
avoided maintaining a conduit-specific Grafana Docker image, but made
packaging dashboard json files cumbersome.
Roll our own Grafana Docker image, that includes conduit-specific
dashboard json files. This significantly decreases the `conduit install`
output size, and enables dashboard integration in the docker-compose
environment.
Fixes#567
Part of #420
Signed-off-by: Andrew Seigner <siggy@buoyant.io>