Make sure checkpoint listeners are always notified

The `IVoldCheckpointListener`s should be notified when checkpointing
completes and when vold becomes aware that no checkpoint will be
required. We were previously not notifying in the case where reading
kMetadataCPFile returned `false` (error while reading) which tells vold
there isn't a checkpoint. Refactored `cp_needsCheckpoint` to make sure
this case isn't missed.

Bug: 362567323
Test: m && ./vendor/google/tools/flashall && adb wait-for-device && adb reboot && adb wait-for-device && adb logcat -s storageproxyd:v vold:V Checkpoint:V
Change-Id: I55a4b908655446517b961bb1affdae694b76a70d
1 file changed