tests: add field sizes to inode/super struct tests

tests: add field sizes to inode/super struct tests

In addition to validating the ordering of fields within the inode
and superblock structures, also validate the field sizes.  Otherwise
it is possible to incorrectly change the size of one of these fields
without getting any kind of error from these tests.  Failures would
only show up later in the test image checks if the field that is
changed is before another in-use field.

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>