Fix regression on compile and upload with attached sketches (#545)

* fix regression on board attach

* fix integration tests

cli/upload/upload.go

-/*
- * This file is part of arduino-cli.
- *
- * Copyright 2018 ARDUINO SA (http://www.arduino.cc/)
- *
- * This software is released under the GNU General Public License version 3,
- * which covers the main part of arduino-cli.
- * The terms of this license can be found at:
- * https://www.gnu.org/licenses/gpl-3.0.en.html
- *
- * You can be released from the requirements of the above licenses by purchasing
- * a commercial license. Buying such a license is mandatory if you want to modify or
- * otherwise use the software for commercial activities involving the Arduino
- * software without disclosing the source code of your own applications. To purchase
- * a commercial license, send an email to license@arduino.cc.
- */
+// This file is part of arduino-cli.
+//
+// Copyright 2020 ARDUINO SA (http://www.arduino.cc/)
+//
+// This software is released under the GNU General Public License version 3,
+// which covers the main part of arduino-cli.
+// The terms of this license can be found at:
+// https://www.gnu.org/licenses/gpl-3.0.en.html
+//
+// You can be released from the requirements of the above licenses by purchasing
+// a commercial license. Buying such a license is mandatory if you want to
+// modify or otherwise use the software for commercial activities involving the
+// Arduino software without disclosing the source code of your own applications.
+// To purchase a commercial license, send an email to license@arduino.cc.
 
 package upload
 
@@ -56,6 +54,8 @@ func NewCommand() *cobra.Command {
 	uploadCommand.Flags().BoolVarP(&verify, "verify", "t", false, "Verify uploaded binary after the upload.")
 	uploadCommand.Flags().BoolVarP(&verbose, "verbose", "v", false, "Optional, turns on verbose mode.")
 
+	uploadCommand.MarkFlagRequired("port")
+
 	return uploadCommand
 }