Fix tests for new overlayfs

adb remount used to remount every full or almost full partition.
However, this is not possible with new overlayfs because it would
require a very permissive overlay_remounter policy.

Make component of test that specifically looks for that logging only

Bug: 397158623
Test: system/core/fs_mgr/tests/adb-remount-test.sh on Pixel 6
Change-Id: I0a1d8088fa0a3ce880111254366468268c6bffb9