Unable to enable Graphite through environment variable

When trying to the run the `1.6.4` [Dockerfile](https://github.com/influxdata/influxdata-docker/blob/master/influxdb/1.6/Dockerfile) with Graphite, it seems to be ignoring the environment variables when set in a `docker-compose` file.

My settings are as follows:
```
environment:
- VIRTUAL_HOST=influxdb
- INFLUXDB_GRAPHITE_ENABLED=true
```

But when I look at the `influxdb.conf` it reports back as `graphite enabled = false`

(Using the alpine version of `1.6.4` appears to not have the same problem)

Start with influxdb/1.6/Dockerfile and compare it with the Alpine 1.6.4 image configuration. Reproduce the docker-compose environment settings, inspect the resulting influxdb.conf, and determine what needs to change so INFLUXDB_GRAPHITE_ENABLED=true is honored.

Written by the indexing model from the issue text.