use self.user instead of @user in message for rails 3 compatibility

Change-Id: Iac4e81744bb89a73c6a0dc8414d503f59e54df2a
Reviewed-on: https://gerrit.instructure.com/28425
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>
QA-Review: James Williams  <jamesw@instructure.com>
Product-Review: James Williams  <jamesw@instructure.com>