The BDRV_REQ_FUA flag can trivially be allowed in the crypt driver
as a passthrough to the underlying block driver.

Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-id: 20170927125340.12360-7-berrange@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>