node_features/knl_cray use cnselect rather than capmc

node_features/knl_cray plugin modified to get current node NUMA mode using
    cnselect command rather than capmc command. This gets the current
    BIOS setting, which could differ from what is configured to be
    set on boot, at least if something other than Slurm is modifying
    KNL modes.
bug 2850