Require root or runner privs to run `ping` command

Addresses: basho/riak#561

In certain cases, if `riak ping` was run before `riak start` (or any
other command) a `.erlang.cookie` file was created with the wrong
privs (in this case a root user) that prevented the riak user from
starting erlang.
Merge pull request #146 from basho/jem-source-default-scripts

Require root or runner privs to run `ping` command