Currently e2image metadata image handling and creating is completely
broken on big endian systems. It just does not care about endianness at
all. This was uncovered With addition of i_bitmaps test, which is the
first test that actually tests e2image metadata image.
Fix it by making sure that all on-disk metadata that we write and read
to/from the metadata image is properly converted.
Signed-off-by: Lukas Czerner <lczerner@redhat.com>