Improve checksum performance for images
Improve checksum performance for images

Do md5 and sha256 in parallel to speed things up for larger images.

Change-Id: Ib782fe54e4286ba2749a7ab7247f5d41a887a370
Signed-off-by: Paul Belanger <e7139c8e6c4ea75cc1c287ce081b2dc0f3ab39ec@redhat.com>

switch-ch/diskimage-builder,openstack/diskimage-builder,switch-ch/diskimage-builder,openstack/diskimage-builder