ImageManager returns FiemapStatus.

IImageManager::CreateBackingImage and ZeroFillNewImage now returns
FiemapStatus, which is an error code and provides more information
about the reason of error.

In particular, the error code is NO_SPACE if disk space is full during
allocation / writing.

Bug: 138808058
Test: libsnapshot_test

Change-Id: I500a3d9f55a2d7e60438b5b4ae70f8b5fed162fa