userportal: prevent an error dialog in login page

Frontend -> handleActionResult:
* Removed the redundant call to
  getEventsHandler().runActionFailed(failed) which invokes an error
  dialog without verifying 'isRaiseErrorModalPanel' flag first.
* Removed the method as well since it's not used anymore.
* Now, the error dialog will be invoked only after flag verification
  by raising frontendFailureEvent.
* This issue of duplicate dialog invocation was hidden by now
  in UserPortal's login page by simply ignoring any error
  dialog (removed in Ibd2718649ab4031e6ff2b0d0e6c449f53164ff9f).

Change-Id: Ib240214df319a0122ebcac82bf2b96d608997432
Bug-Url: https://bugzilla.redhat.com/957793
Signed-off-by: Daniel Erez <derez@redhat.com>