virsh: Create macro for common "network" option
    
    Rather than continually cut-n-paste the strings into each command,
    create a common macro to be used generically.  Note that not all
    '{.name = "network",' entries are replaced, just those that have the
    common .help string of "network name or uuid".
    
    Signed-off-by: John Ferlan <jferlan@redhat.com>