Datadog output plugin logs API key

[bobmshannon]

Bug report

When using the datadog output plugin, telegraf can log the datadog API key if the server is unreachable or in any scenario where debug information is logged that includes the HTTP query URI.

Relevant telegraf.conf:

Any configuration with the Datadog output plugin enabled.

System info:

Telegraf version 1.4.3

Expected behavior:

The API key should not be logged. In many cases, logs are aggregated in a central system viewable by multiple operators, and including sensitive information such as API keys is not ideal from a security standpoint.

Actual behavior:

The API key is logged:

Nov 02 07:13:03 x.x.x.x telegraf[722]: 2017-11-02T07:13:03Z W! Skipping a scheduled flush because there is already a flush ongoing.
Nov 02 07:14:03 x.x.x.x telegraf[722]: 2017-11-02T07:14:03Z W! Skipping a scheduled flush because there is already a flush ongoing.
Nov 02 07:28:03 x.x.x.x telegraf[722]: 2017-11-02T07:28:03Z W! Skipping a scheduled flush because there is already a flush ongoing.
Nov 02 07:29:33 x.x.x.x telegraf[722]: 2017-11-02T07:29:33Z W! Skipping a scheduled flush because there is already a flush ongoing.
Nov 02 07:35:33 x.x.x.x telegraf[722]: 2017-11-02T07:35:33Z W! Skipping a scheduled flush because there is already a flush ongoing.
Nov 02 07:35:33 x.x.x.x telegraf[722]: 2017-11-02T07:35:33Z E! Error writing to output [datadog]: error POSTing metrics, Post https://app.datadoghq.com/api/v1/series?api_key=<<SNIPPED>>
Nov 02 07:35:48 x.x.x.x telegraf[722]: 2017-11-02T07:35:48Z E! Error writing to output [datadog]: error POSTing metrics, Post https://app.datadoghq.com/api/v1/series?api_key=<<SNIPPED>>
Nov 02 07:36:03 x.x.x.x telegraf[722]: 2017-11-02T07:36:03Z W! Skipping a scheduled flush because there is already a flush ongoing.
Nov 02 07:36:05 x.x.x.x telegraf[722]: 2017-11-02T07:36:05Z E! Error writing to output [datadog]: error POSTing metrics, Post https://app.datadoghq.com/api/v1/series?api_key=<<SNIPPED>>
Nov 02 07:36:19 x.x.x.x telegraf[722]: 2017-11-02T07:36:19Z E! Error writing to output [datadog]: error POSTing metrics, Post https://app.datadoghq.com/api/v1/series?api_key=<<SNIPPED>>