Add KEY_ENABLE_WHEN_COMPLETED for testing

Per design, we ask user's confirmation before enabling DSU when
install completed. To simplify the process of testing, this CL adds
a paramenter (intent key) "KEY_ENABLE_WHEN_COMPLETED". If the key is
set, the installation service will not ask user before enabling DSU.

Bug: 131866826
Test: adb shell am start-activity -n com.android.dynsystem/com.android.dynsystem.VerificationActivity
      -a android.os.image.action.START_INSTALL
      -d file:///storage/emulated/0/Download/system.raw.gz
      --el KEY_SYSTEM_SIZE 893841408
      --el KEY_USERDATA_SIZE 8589934592
      --ez KEY_ENABLE_WHEN_COMPLETED true

Change-Id: Id38c4c0525199594f6bd6704b5a575d4a42b7b61