Split installing from display result.

This allows us to properly deal with the activity lifecycle of this
step.

Note: If the activity is destroyed while the installation finishes we do
not pick up the result. This bug was there before.

Test: - Canceled during write-to-package-installer and
        package-installer-process phase
      - Resized during both phases too.

Change-Id: Ieecd37b62f4e946976fbe7d028a44140cf47b881