fix masquerading for accounts with custom dashboards

fixes CAT-637

Test plan:
 1. Set a custom dashboard for an account:
    a = Account.find(x)
    a.settings[:dashboard_url] = 'http://some-url'
    a.save!
 2. Clicking the logo in the top left should still take you
    to your custom dashboard, however..
 3. Clicking "Become" on a user's profile page should start
    a masquerading session

Change-Id: Ibe60f2a6fb80b21ca58251f3f02591c1bb7ec9b6
Reviewed-on: https://gerrit.instructure.com/43559
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Jeff Belser <jbelser@instructure.com>
Reviewed-by: Jeff Belser <jbelser@instructure.com>
QA-Review: Jeff Belser <jbelser@instructure.com>
Tested-by: Jeff Belser <jbelser@instructure.com>
Product-Review: Adam Phillipps <adam@instructure.com>
QA-Review: Adam Phillipps <adam@instructure.com>

app/helpers/application_helper.rb

@@ -823,12 +823,12 @@ module ApplicationHelper
   end
 
   def dashboard_url(opts={})
-    return super(opts) if opts[:login_success]
+    return super(opts) if opts[:login_success] || opts[:become_user_id]
     custom_dashboard_url || super(opts)
   end
 
   def dashboard_path(opts={})
-    return super(opts) if opts[:login_success]
+    return super(opts) if opts[:login_success] || opts[:become_user_id]
     custom_dashboard_url || super(opts)
   end
 

spec/helpers/application_helper_spec.rb

@@ -477,8 +477,16 @@ describe ApplicationHelper do
         expect(dashboard_url).to eq "http://foo.bar"
       end
 
-      it "with login_success=1, returns a regular canvas dashboard url" do
-        expect(dashboard_url(:login_success => '1')).to eq "http://test.host/?login_success=1"
+      context "with login_success=1" do
+        it "returns a regular canvas dashboard url" do
+          expect(dashboard_url(:login_success => '1')).to eq "http://test.host/?login_success=1"
+        end
+      end
+
+      context "with become_user_id=1" do
+        it "returns a regular canvas dashboard url for masquerading" do
+          expect(dashboard_url(:become_user_id => '1')).to eq "http://test.host/?become_user_id=1"
+        end
       end
 
       context "with a user logged in" do