student.tests: Added db access in mock_render_to_response() to test any issues with @transaction.commit_manually
student.views.confirm_email_change: commit/rollback transaction after rendering response instead of before
Merge pull request #1345 from edx/usman/lms1222-email-confirm-transaction-errors

Commit/rollback transaction after rendering response to prevent TransactionManagementErrors due to db access in templates.