Hi,

first thanks for this awesome software. But I have some trouble and I don't know how to proceed. First I try to find out what else I could provide for this report to be a good bug report.

First, I use the latest version (v1.14.0) from openSUSE build Service. I know, I should compile it by my self to avoid any other causes for this behavior. But for now I still use this package from there

What happened:

The current preview endpoint (/api/v1/rule/test/<grafana | datasourceUID>) does not return a very structured response that enables us to visualize labels and values during the preview step in the alert creation.

The JSON response below encode this information in a stringified format.

This would enable us to move forward with grafana/grafana#4

Bug Description
fix issues found by Coverity Scan in syncMain.c

To Reproduce
N/A

Expected Behavior
fix following issues:
| issue type | category | file path | function | line number |
| -------------------------- | -------------------------- | -------------------------- | -------------------------- |

Relevant telegraf.conf:

[[inputs.openweathermap]]
  app_id = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
  

Describe the Bug

The JSON response sent back over HTTP doesn't encode certain characters correctly.

For example, if a value in a string column contains the char \1 the byte value is copied verbatim in the response, breaking the client:

>>> json.loads('"\1"')
...
json.decoder.JSONDecodeError: Invalid control character at: line 1 column 2 (char 1)

Instead, we shou