Suppress duplicate selection of value for ping
Per discussion here
https://github.com/cfengine/core/pull/373#issuecomment-13969241
It makes sense for identical os paths to be grouped, but if there is any
difference in a path it should be seperated to avoid context soup. So I
have moved ping into each os context and while doing that alphabatized
the commands.
Merge pull request #394 from nickanderson/feature/masterfiles/libraries/stdlib/paths/suppress_duplicate_ping

cfengine_stdlib.cf: Suppress duplicate selection of value for ping