rgmanager: Clear vm.sh default
    
    The default behavior of vm.sh is to use_virsh whenever
    possible.  The problem with specifying a default in the
    RA metadata is that it causes rgmanager to provide a
    value to the RA when it is called.  In this case, rgmanager
    was providing "1" as the default, meaning that the logic
    which carefully determines whether to use 'xm' or 'virsh'
    is disabled.
    
    This is not seen when testing the resource agent by
    hand; it is only seen when called in the context of
    rgmanager or rg_test.
    
    Resolves: rhbz#545916
    
    Signed-off-by: Lon Hohberger <lhh@redhat.com>