Reduce jank on incoming phone call during dream.

- Include dreams in the conditions that disable transition animations.
  This way there is no visibility of activities that are closing
  behind the keyguard when an activity that dismisses the keyguard
  starts up.

- Do not notify the keyguard mediator when the keyguard is dismissed
  because a dream is starting up. This keeps activities from resuming
  just because the keyguard is being dismissed.

Fixes bug 11064847.

Change-Id: I9d32fc96d518b1cdab511e187226a3cb889cf6d4