Disable <Choose a Role> option to prevent error while adding Group

Fixes https://bugzilla.redhat.com/show_bug.cgi?id=1730402

app/controllers/ops_controller/ops_rbac.rb

@@ -1169,11 +1169,7 @@ def rbac_group_set_form_vars
     Rbac::Filterer.filtered(MiqUserRole).each do |r|
       @edit[:roles][r.name] = r.id
     end
-    @edit[:new][:role] = if @group.miq_user_role.nil? # If adding, set to first role
-                           @edit[:roles][@edit[:roles].keys.sort[0]]
-                         else
-                           @group.miq_user_role.id
-                         end
+    @edit[:new][:role] = @group.miq_user_role ? @group.miq_user_role.id : @edit[:roles].first
 
     all_tenants, all_projects = Tenant.tenant_and_project_names
     placeholder_text_tenant = _('Choose a Project/Tenant')

app/views/ops/_rbac_group_details.html.haml

@@ -70,8 +70,8 @@
             = link_to(@group.miq_user_role.name, "#", params)
         - else
           = select_tag('group_role',
-              options_for_select(@edit[:roles].sort, @edit[:new][:role]),
-              :class  => "selectpicker")
+                       options_for_select(@edit[:roles].sort, selected: @edit[:new][:role], disabled: ["<Choose a Role>", nil]),
+                       :class => "selectpicker")
           :javascript
             miqInitSelectPicker();
             miqSelectPickerEvent("group_role", "#{combo_url}")