CLEANUP: cfgparse-global: move "node" and "description" to their own parser

CLEANUP: cfgparse-global: move "node" and "description" to their own parser

Both keywords give an name/desc to the current node, so they were moved
together to a new cfg_parse_global_node_desc() function and registered in
cfg_kws so as to become discoverable via "-dKcfg".

While doing this, a test on strdup(node) result was added so as to fail
cleanly on memory allocation failure (this remains i nthe scope of a
cleanup since in practice it never happens).