test(nodestat): pin the fping option and the usemon abbreviations

Add a unit test for the option that selects fping instead of nmap.

The test takes the specification out of the plugin source and gives it to
Getopt::Long with the settings that the daemon uses, so it drives the
specification that the plugin ships.

It shows that -f, --usefping and the older --useping each select fping, that
--use and --us still select usemon and do not select fping, that the bundles
-mf and -fm select both options, and that both places parse through the one
specification.