Change activitymanager start condition

:Release Notes:
Change activitymanager start condition to be on rest-boot-done

:Detailed Notes:
In order to have a stable and fast boot sequence for the last input app,
the start condition of activitymanager should be changed.
Activitymanager can be deferred because it isn't related to the last
input app.

Here are the boot conditions:
- core-boot-done: Very important services for factory line
- datastore-init-start: DB8, SettingsServices, and filecache
- init-boot-done: The services which needed for last-input-app
- minimal-boot-done: The services which needed for app launching
- rest-boot-done: Other services which can be deferred
- boot-done: Boot complete (== for renice jobs in boottime)

:Testing Performed:
- #434 + this commit
- activitmanager works fine in auto mode

:QA Notes:

:Issues Addressed:
[GF-44168] [Boottime] Optimize boot sequence

Open-webOS-DCO-1.0-Signed-off-by: Sangwoo Kang <sangwoo82.kang@lge.com>
Change-Id: I44188163c6d0ba699258b46644cb314465778d82
Reviewed-on: https://g2g.palm.com/3951
Reviewed-by: DCO Verification
Reviewed-by: Herb Kuta <herb.kuta@lge.com>
Tested-by: Herb Kuta <herb.kuta@lge.com>
Reviewed-by: Maksym Sditanov <maxim.sditanov@lge.com>
Tested-by: Maksym Sditanov <maxim.sditanov@lge.com>