Check go version in cmd/scw too

Author: Quentin Perez

cmd/scw/main.go

@@ -3,6 +3,9 @@
 // license that can be found in the LICENSE.md file.
 
 // Manage BareMetal Servers from Command Line (as easily as with Docker)
+
+// +build go1.5
+
 package main
 
 import (

cmd/scw/main_unsupported.go

@@ -0,0 +1,7 @@
+// +build !go1.5
+
+package main
+
+func error() {
+	`Bad go version, please install a version greater than or equal to 1.5`
+}