fixed generation of gossipinfo JSON response to avoid having a hostname and IP for one node. This led to false positive replacement exceptions.
this builds on Netflix/Priam#345 in correcting gossipinfo rest response. altered the bit that parses the JMX gossipinfo response into JSON, into something I feel a bit better about... Beefed up the unit tests, look for the inner top and bottom items, and a common value across all 3. verify the proper number of items as well. This should address the issue in Netflix/Priam#348 for builds past about 1.2.28, where replacement IP was changed to look to a peers gossipinfo.
Merge pull request #350 from jhohertz/ginfo-fix

Fixes to gossipinfo to prevent operational issues w/ node replacements