Avoid making the user ID dir under system_ce in ATMS

The parent directory of recent_images (system_ce/<user_id>) is managed
by other system services, and isn't available until the corresponding
user is fully unlocked. Avoid trying to make that folder if that doesn't
exist.

Also fail the directory creation if it isn't a directory, and we can't
create it for recent_images.

Bug: 288146194
Test: Recent images and launch params folders are still created when
necessary.
Test: atest LaunchParamsPersisterTests

Change-Id: I7e8e3167e3aea60f6426e5ca3571e3fb1dad98e0