Fix dashboard template around final grade status

* ae8847cd6e73 checked in buggy conditional in the dashboard templates
  that caused an empty 'details being wrapped up' box to display
  regardless of whether it was true.
* Simplify conditional so that we care only whether output of the view's
  _cert_info() says 'processing', which should be the value computed when
  either no cert status exists or when the certs are, in fact processing.

  This should mean that the "details being wrapped up" message is
  displayed when certs haven't run and the grade box is displayed the
  rest of the time.
Merge pull request #3629 from edx/jrbl/oops-fix-dashboard-template

Fix dashboard template around final grade status