Implement a per-output fixed size metric buffer

Also moved some objects out of config.go and put them in their own
package, internal/models

fixes #568
closes #285

plugins/inputs/influxdb/influxdb.go

@@ -130,7 +130,7 @@ func (i *InfluxDB) gatherURL(
 		p.Tags["url"] = url
 
 		acc.AddFields(
-			p.Name,
+			"influxdb_"+p.Name,
 			p.Values,
 			p.Tags,
 		)

plugins/inputs/influxdb/influxdb_test.go

@@ -84,7 +84,7 @@ func TestBasic(t *testing.T) {
 		"id":  "ex1",
 		"url": fakeServer.URL + "/endpoint",
 	}
-	acc.AssertContainsTaggedFields(t, "foo", fields, tags)
+	acc.AssertContainsTaggedFields(t, "influxdb_foo", fields, tags)
 
 	fields = map[string]interface{}{
 		"x": "x",
@@ -93,5 +93,5 @@ func TestBasic(t *testing.T) {
 		"id":  "ex2",
 		"url": fakeServer.URL + "/endpoint",
 	}
-	acc.AssertContainsTaggedFields(t, "bar", fields, tags)
+	acc.AssertContainsTaggedFields(t, "influxdb_bar", fields, tags)
 }