Use correct location for qcow1 encryption header
    
    After the 8-byte size header, there are two one-byte headers
    and two bytes of padding before the crypt_header field.
    
    Our QCOW1_HDR_CRYPT constant did not skip the padding.
    http://git.qemu.org/?p=qemu.git;a=blob;f=block/qcow.c;h=ece22697#l41
    
    https://bugzilla.redhat.com/show_bug.cgi?id=1185165