Fix a nil dereference in DataplaneClient.getReq().

This was a case of golang's wonderfully confusing nil pointer vs
nil interface.

pkg/haproxy/dataplane.go

@@ -171,11 +171,17 @@ func drainAndClose(body io.ReadCloser) {
 }
 
 func (client *DataplaneClient) getReq(
-	path, method string, body io.Reader) (*http.Request, error) {
-
+	path, method string,
+	body io.Reader,
+	withbody bool,
+) (req *http.Request, err error) {
 	relPath := &url.URL{Path: path}
 	url := client.baseURL.ResolveReference(relPath)
-	req, err := http.NewRequest(method, url.String(), body)
+	if withbody {
+		req, err = http.NewRequest(method, url.String(), body)
+	} else {
+		req, err = http.NewRequest(method, url.String(), nil)
+	}
 	if err != nil {
 		return req, err
 	}
@@ -238,7 +244,7 @@ func (client *DataplaneClient) StartTx(
 	// req.URL.RawQuery = query.Encode()
 	// req.Header.Set("Accept", "application/json")
 
-	req, err := client.getReq(txPath, http.MethodPost, nil)
+	req, err := client.getReq(txPath, http.MethodPost, nil, false)
 	if err != nil {
 		return
 	}
@@ -292,7 +298,7 @@ func (client *DataplaneClient) FinishTx(
 	// req.Header.Set("Accept", "application/json")
 
 	state := ReloadState{Status: Unknown}
-	req, err := client.getReq(txPath+"/"+tx.ID, http.MethodPut, nil)
+	req, err := client.getReq(txPath+"/"+tx.ID, http.MethodPut, nil, false)
 	if err != nil {
 		return state, err
 	}
@@ -404,7 +410,8 @@ func (client *DataplaneClient) configTLS(
 	// req.URL.RawQuery = query.Encode()
 	// req.SetBasicAuth(client.user, client.password)
 	// req.Header.Set("Accept", "application/json")
-	req, err := client.getReq(path, method, rdr)
+	req, err := client.getReq(path, method, rdr,
+		method != http.MethodDelete)
 	if err != nil {
 		return err
 	}
@@ -499,7 +506,8 @@ func (client *DataplaneClient) DeleteTx(tx *models.Transaction) error {
 
 func (client *DataplaneClient) Reloaded(id string) (bool, ReloadState, error) {
 	state := ReloadState{ID: id}
-	req, err := client.getReq(reloadsPath+"/"+id, http.MethodGet, nil)
+	req, err := client.getReq(reloadsPath+"/"+id, http.MethodGet, nil,
+		false)
 	if err != nil {
 		return false, state, err
 	}