Use cache for http.client in tsdb package. (#6833)

* datasource: move caching closer to datasource struct

* tsdb: use cached version of datasource http transport

closes #6825

pkg/tsdb/models.go

@@ -2,6 +2,7 @@ package tsdb
 
 import (
 	"github.com/grafana/grafana/pkg/components/simplejson"
+	"github.com/grafana/grafana/pkg/models"
 	"gopkg.in/guregu/null.v3"
 )
 
@@ -9,7 +10,7 @@ type Query struct {
 	RefId         string
 	Model         *simplejson.Json
 	Depends       []string
-	DataSource    *DataSourceInfo
+	DataSource    *models.DataSource
 	Results       []*TimeSeries
 	Exclude       bool
 	MaxDataPoints int64
@@ -28,20 +29,6 @@ type Response struct {
 	Results      map[string]*QueryResult `json:"results"`
 }
 
-type DataSourceInfo struct {
-	Id                int64
-	Name              string
-	PluginId          string
-	Url               string
-	Password          string
-	User              string
-	Database          string
-	BasicAuth         bool
-	BasicAuthUser     string
-	BasicAuthPassword string
-	JsonData          *simplejson.Json
-}
-
 type BatchTiming struct {
 	TimeElapsed int64
 }