tool_cfgable: Removed list_engine flag from config structure

In preparation for separating the global config options from the per
operation config options, reworked the list engines code to not use a
member variable in the Configurable structure.

src/tool_getparam.h

@@ -30,6 +30,7 @@ typedef enum {
   PARAM_REQUIRES_PARAMETER,
   PARAM_BAD_USE,
   PARAM_HELP_REQUESTED,
+  PARAM_ENGINES_REQUESTED,
   PARAM_GOT_EXTRA_PARAMETER,
   PARAM_BAD_NUMERIC,
   PARAM_NEGATIVE_NUMERIC,