TT#4671 release_dashboard: set default_release to 'none'

* useful for trunk builds

Change-Id: I6b95dbe2b053c530d998081acf9950eb4bfb9563

release_dashboard/static/release_dashboard/js/build.js

@@ -34,7 +34,7 @@ $('select#common_select').change(function() {
   if(version.length > 0) {
     $('input#version_release').val("release-" + version);
   } else {
-    $('input#version_release').val('');
+    $('input#version_release').val('none');
   }
 });
 

release_dashboard/templates/release_dashboard/build_content.html

@@ -23,7 +23,8 @@
         <div class="form-group">
             <label for="version_release">Release version</label>
             <input class="form-control" id="version_release"
-                name="version_release" type="text" value="">
+                name="version_release" type="text"
+                value="none">
         </div>
         <div class="form-group">
             <label for="distribution">Debian release</label>