Don't abort propagation job abortions synchronously from finished

Don't abort propagation job abortions synchronously from finished

This leads to crashes since we changed the connection to the parent
jobs not to be queued anymore.
We don't really need to bubble up the finished state through
parents in that case, and it would also mean that we'd recurse
all the way through leaves as we go up to each parent. So just call
abort directly on the OwncloudPropagator and make sure the abortion
call is posted to the event loop.