Riaknostic used to be a separate app, but it is now embedded with Riak,
so it doesn't make sense to check for tool output if the node is down,
as that mean riaknostic is not available either.
In Riak 1.3.0 riaknostic was included by default. These
tests assumed riaknostic was *not* installed and would
fail on 1.3+ nodes. This change fixes that and refactors
the test to be a little more readable.