Forbid creation of groups with a path length < 5

This restriction does not apply to admins.

app/controllers/groups_controller.rb

@@ -24,6 +24,8 @@ class GroupsController < Groups::ApplicationController
 
   before_action :user_actions, only: [:show]
 
+  before_filter :validate_name, only: :create
+
   skip_cross_project_access_check :index, :new, :create, :edit, :update,
                                   :destroy, :projects
   # When loading show as an atom feed, we render events that could leak cross
@@ -193,6 +195,14 @@ class GroupsController < Groups::ApplicationController
     end
   end
 
+  def validate_name
+    @group = Group.new(group_params)
+    unless @group.path.empty? || @group.path.length > 4 || current_user.admin?
+      flash.now[:alert] = 'Path must have at least a length of 5.'
+      render action: "new"
+    end
+  end
+
   def build_canonical_path(group)
     return group_path(group) if action_name == 'show' # root group path