When checking IsUnreliablePinningAllowed, the existing code calls
IsTestDir on a value starts with "/data", but IsTestDir expects
metadata_dir_. Fix it.
Also, make subdir checks more robust and add test cases for IsSubdir.
Fixes: 162557082
Test: vts_libsnapshot_test
Test: fiemap_image_test
Change-Id: I495cfae3da11d1e0800b8abf520df10dd9a29dce
Add variants to SplitFiemap::Create and FiemapWriter::Open that
returns a FiemapStatus and take a unique_ptr<T>* out parameter to
get more information on the reason of the failure.
Test: fiemap_writer_test
Test: fiemap_image_test
Bug: 138808058
Change-Id: Iea77ac9810f98c2202e038b7aede15dd2d137b2b