fix rendering of account groups when you don't have permission to manage them

test plan:
 * create an admin that has read roster permission only
 * as that user, you should be able to go to /accounts/X/groups, and not
   error

Change-Id: I396d99f971cdbd2dd37b8e9a5a5d7ff578fe9667
Reviewed-on: https://gerrit.instructure.com/29009
Reviewed-by: Jacob Fugal <jacob@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: August Thornton <august@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>

app/views/groups/context_groups.html.erb

@@ -2,7 +2,7 @@
 
 <% content_for :right_side do %>
   <div class="rs-margin-lr rs-margin-top">
-    <% if @context.allow_student_organized_groups %>
+    <% if @context.respond_to?(:allow_student_organized_groups) && @context.allow_student_organized_groups %>
       <% if can_do(@context.groups.new, @current_user, :create) %>
         <a href="#" class="btn button-sidebar-wide add_group_link icon-add"><%= t 'actions.add', 'Start a New Group' %></a>
       <% end %>

spec/views/groups/context_groups.html.erb_spec.rb

@@ -27,5 +27,12 @@ describe "/groups/context_groups" do
     render "groups/context_groups"
     response.should_not be_nil
   end
+
+  it "should render for an account" do
+    view_context(Account.default)
+
+    render "groups/context_groups"
+    response.should_not be_nil
+  end
 end