further process management changes

Increase timeout for waiting for init:stop/0 to stop nodes from an extra
second to 10 extra seconds. Be sure to wait until the timeout expires
before using kill on any nodes that fail to stop. To avoid unconditionally
waiting the full timeout period, use kill -0 where possible to watch for
nodes stopping. Use kill -9 only after the full timeout period has elapsed
and the node still hasn't stopped. Fix setting of the cookie when
converting the riak_test node to a distributed node.
Merge pull request #568 from basho/vinoski/nicer-kills2

further process management changes