Checks for ElasticSearch 0.9x and 1.x

/_cluster/nodes/_local has been retired with ES 1.0, so this check does
not work anymore.
By identifying the cluster version before running the check,
we can adjust the URL.
More explicit name for method fetching ES version.
Merge pull request #550 from cotap/master

Checks for ElasticSearch 0.9x and 1.x