Add `getpid` command to nodetool and add missing options
Add `getpid` command to nodetool and add missing options

Adds `getpid` as a way to get the PID of the running node.  This
also options that were missing from the usage text.

Supports #251

glickbot/riak,basho/riak,DavidAlphaFox/riak,xuejianhai/riak,elkingtonmcb/riak,biddyweb/riak,yangchengjian/riak,laurenrother/riak,GabrielNicolasAvellaneda/riak,amyvmiwei/riak,authbox-lib/riak