Running kapacitor without connecting to influxdb

I want to run an instance using the latest version of kapacitor image without connecting to influxdb

**Expectation:**
When running version 1.5.9 and modifying a environment variable to disable the subscriptions, like so:
```
docker run -p 9092:9092 -e KAPACITOR_INFLUXDB_0_DISABLE_SUBSCRIPTIONS=true \
kapacitor:1.5.9
```
it runs a kapacitor instance. It works, great!

**Result:**
When I want to upgrade the version of the image to 1.6.6, I expect the same result as above, but instead I get this
```
failed to connect to InfluxDB, retrying..." service=influxdb
cluster=default err="Get \"http://localhost:8086/ping\":
dial tcp 127.0.0.1:8086: connect: connection refused
```

Start with the Docker invocation using kapacitor:1.5.9 and KAPACITOR_INFLUXDB_0_DISABLE_SUBSCRIPTIONS=true, then compare its behavior with kapacitor:1.6.6 and the reported InfluxDB connection error. Done means the 1.6.6 image starts on port 9092 without an InfluxDB connection when subscriptions are disabled.

Written by the indexing model from the issue text.