This modification is in order to avoid multiple writes
    and/or updates when there is no changes.

    Part of the logic in updateVulnerability was optimized.
    Add differ.applyIfChanged and callInTransaction.

    SynchronizeVulnerability returns null if there is nothing
    to synchronize.

    Some modifications were needed to couple with new logic.
    e.g. if (SynchronizeVulnerability = null) continue.

    Test are provided.

Signed-off-by: Andres Tito <[email protected]>

-Remove unnecesary persistance in updateVulnerability function.
-Return updated exisitingVulnerability in updateVulnerability
-Remove return of empty vulnerability
-Wrap synchronizedVUlnerability in callInTransaction to share
same transaction.

Signed-off-by: Andres Tito <[email protected]>