cmd Kapacitor help message for service-tests returns help information for vars

$ kapacitor help service-tests
Usage: kapacitor vars

Print debug vars in JSON format.

$ kapacitor help vars
Usage: kapacitor vars

Print debug vars in JSON format.

See also line 311-314 in cmd/kapacitor/main.go (I'm looking at commit fcce3ee9e6abcee5595fd61066bfc904edb1e113 in master)

```golang
...
case "vars":
varsUsage()
case "service-tests":
varsUsage()
...
```

Start at cmd/kapacitor/main.go lines 311-314 and inspect the help handlers for vars and service-tests. Make the service-tests help output describe service-tests rather than vars, then run both help commands and verify that vars still reports its own usage.

Written by the indexing model from the issue text.