Changed to not force default netvm in Create New VM

To avoid conflict with scripts that make whonix magic,
if the user selects default netvm, we do not set any  netvm and
trust the create_vm method to properly set it as default appropriate
for the given template.

fixes QubesOS/qubes-issues#1954

qubesmanager/create_new_vm.py

@@ -154,7 +154,8 @@ class NewVmDlg(QtGui.QDialog, Ui_NewVMDlg):
 
         properties = {}
         properties['provides_network'] = self.provides_network.isChecked()
-        properties['netvm'] = self.netvm_list[self.netvm.currentIndex()]
+        if self.netvm.currentIndex() != 0:
+            properties['netvm'] = self.netvm_list[self.netvm.currentIndex()]
         if self.install_system.isChecked():
             properties['virt_mode'] = 'hvm'
             properties['kernel'] = None