power/cray work

Correct capmc arguments to set power cap.
Convert "capmc get_node_energy_counter" to use hostlist expressin rather
   than listing every node in a comma separated list.
Log commands and args run by the plugin via the power_run_script()
   function in src/plugins/power/common/power_common.c.
Use hostlist to build condenced nid list for power cap set/clear functions.