Fix coverity complain in commandtest.c
    
    For a "newfd1" the coverity tools thinks that the fd is closed in
    a "virCommandPassFD", but with "flags == 0" it cannot be closed.
    
    The code itself is ok, but coverity tool thinks that there is
    "double_close" of the "newfd1" and to prevent showing this error
    we simply add a comment before the proper close.
    
    This has been found by coverity.
    
    Signed-off-by: Pavel Hrdina <phrdina@redhat.com>