LU-15408 sec: confirm encrypted file's hash

LU-15408 sec: confirm encrypted file's hash

It is a good practice to always confirm on server side the encrypted
file's hash included in the digested form sent by the client.

Fixes: ed4a625d88 ("LU-13717 sec: filename encryption - digest support")
Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I42212a36b23e4e6e41184a78fa8244c5e2d8dd1f
Reviewed-on: https://review.whamcloud.com/45964
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Patrick Farrell <pfarrell@whamcloud.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>