Only log restorecon changes for existing dirs.

If we just created an app private data directory, we're always going
to be relabeling it, so don't log in that case.  Continue logging if
something caused us to relabel an existing app data directory.

Test: builds, boots, only logs for existing dirs
Bug: 31958779
Change-Id: Id03f7c18aed191a4c7fb9dcf9380136c93798a4b