ext4: add a test for ea_inode feature

ext4: add a test for ea_inode feature

ea_inode feature supports creating extended attributes with values
greater than the fs block size. This test exercises some common
scenarios:

 - Extended attibute being placed in inode vs xattr block
 - Removing extended attribute
 - Removing a file that has an extended attribute
 - Multiple files having identical large attribute values
 - Repeatedly setting an extended attribute with various sizes

Signed-off-by: Tahsin Erdogan <tahsin@google.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>