powerman: do not always call "all" query script

Problem: When selecting a script to use for an action, the "all"
version of a script is always used if the action is a query action
(e.g. power status query, beacon query, etc.).

This can be problematic in situations where blades/nodes/etc. are
not fully populated, such as in a chassis.  We do not want to query
"all" things in that case.

Solution: Only call the "all" script if it is a query and a singlet
version of the script does not exist.  For device files where
unpopulated nodes may exist, it can define an all script and singlet
script for each scenario.

src/powerman/device.c

@@ -683,8 +683,12 @@ static int _enqueue_targeted_actions(Device * dev, int com, hostlist_t hl,
  pluglist_iterator_destroy(itr);
 
  /* Try _all version of script.
+ *
+ * - use if action is a query, unless no singlet version exists
+ * (i.e. if there is no singlet version, we have to use the _all
+ * version)
  */
- if (all || _is_query_action(com)) {
+ if (all || (_is_query_action(com) && dev->scripts[com] == NULL)) {
  int ncom = _get_all_script(dev, com);
 
  if (ncom != -1) {