qemu-pr-helper: miscellaneous fixes
    
    1) Return a generic sense if TEST UNIT READY does not provide one;
    
    2) Fix two mistakes in copying from the spec.
    
    Cc: qemu-stable@nongnu.org
    Reported-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
    (cherry picked from commit a4a9b6eaf35dbe4bf0e069854945bf5e45fc7eab)
    Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>