Only log when system UID finds missing data paths.

We're really only interested in tracking down when the system UID
tries touching missing data paths, since it's the only one with enough
permissions to mkdirs() directly without going through installd.

Without the guard added in this CL, we'd end up logging for direct
boot aware apps that tried obtaining CE paths while locked, which is
perfectly valid.

Bug: 28272737
Change-Id: Id24f3160f61d8ad8047d5c551bc6a91c868bd301