virsh: Implement "domrename" command
    
    This patch implements new virsh command, domrename.
    
    Using domrename, it will be possible to rename domain from the virsh shell by
    calling virRenameDomain API.
    
    It takes two arguments, current domain name and new domain name.
    
    Example:
    
    virsh # list --all
     Id    Name                           State
     ----------------------------------------------------
      -     bar                            shut off
    
    virsh # domrename bar foo
    Domain successfully renamed
    
    virsh # list --all
     Id    Name                           State
     ----------------------------------------------------
      -     foo                            shut off
    
    virsh #
    
    Signed-off-by: Tomas Meszaros <exo@tty.sk>