LU-11915 deubugfs: add support for xattrs in external inodes

LU-11915 deubugfs: add support for xattrs in external inodes

There was "e2fsck: add support for xattrs in external inodes" before
that added xattr in external inode support to utils. But it was
not applied to the last e2fsprogs version for some reasons.

This patch adds external inode output to debugfs that is required
for conf-sanity 115 test.

Change-Id: I3cfca85e2d34b54030d21fafa12be3dbf30e5b5c
Signed-off-by: Artem Blagodarenko <c17828@cray.com>
Reviewed-on: https://review.whamcloud.com/35417
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Li Dongyang <dongyangli@ddn.com>