Fix subdir caclulation in MountRegistry

+ add tests

Bug: 133436048
Test: atest system/incremental_delivery/incfs
Change-Id: If8f3d08b0048ea15700029726382e0c9fe8fc98c
Merged-In: If8f3d08b0048ea15700029726382e0c9fe8fc98c
3 files changed
tree: eb2b7ba2b1e4bf7795b82c4080bf38947a35f421
  1. incfs/
  2. libdataloader/
  3. .clang-format
  4. PREUPLOAD.cfg