resolves issues where failed api calls lead to obscure errors (#7051)

plugins/inputs/kibana/kibana.go

@@ -3,6 +3,8 @@ package kibana
 import (
 	"encoding/json"
 	"fmt"
+	"io"
+	"io/ioutil"
 	"net/http"
 	"strconv"
 	"strings"
@@ -250,6 +252,12 @@ func (k *Kibana) gatherJsonData(url string, v interface{}) (host string, err err
 
 	defer response.Body.Close()
 
+	if response.StatusCode != http.StatusOK {
+		// ignore the err here; LimitReader returns io.EOF and we're not interested in read errors.
+		body, _ := ioutil.ReadAll(io.LimitReader(response.Body, 200))
+		return request.Host, fmt.Errorf("%s returned HTTP status %s: %q", url, response.Status, body)
+	}
+
 	if err = json.NewDecoder(response.Body).Decode(v); err != nil {
 		return request.Host, err
 	}