[BUG] Consul input plugin does not utilize token

[smolse]

Bug report

Before Consul version 0.7.2 there was no need to include ACL token in request params or headers to get health checks data from Consul API. In version 0.7.2 Consul introduced complete ACL coverage which has been taken into use by default in Consul 0.8.0. Now in order to get health checks data from API a user needs to have a token with node:read and service:read policies . Consul input plugin in telegraf already accepts ACL token as a configuration option, but neither uses it to set in API client config nor passes to the State method.

Relevant telegraf.conf:

[[inputs.consul]]
  address = "localhost:8500"
  token = "<replace me>"

System info:

Telegraf version: any that has consul input plugin
Consul version: >= 0.8.0

Steps to reproduce:

1. Assume consul is running locally with default config and API is available at localhost:8500
2. Create ACL token in Consul and add it to the telegraf config for consul plugin
3. Run telegraf --config telegraf.conf --test

Expected behavior:

Consul plugin was able to retrieve metrics, e.g. the output is:

$ telegraf --config telegraf.conf --test
* Plugin: inputs.consul, Collection 1
> consul_health_checks,node=consul,check_id=serfHealth,host=vbox check_name="Serf Health Status",service_id="",status="passing",passing=1i,critical=0i,warning=0i 1508784579000000000

Actual behavior:

Output is:

$ telegraf --config telegraf.conf --test
* Plugin: inputs.consul, Collection 1

I.e. consul plugin in telegraf is not able to get health states from Consul API.