The image end offset as reported by qemu-img check is different when
using an external data file; we do not care about its value here, so we
can just filter it.  Incidentally, common.rc already has _check_test_img
for us which does exactly that.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-id: 20191107163708.833192-18-mreitz@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>