adding dead snakes to hadoop cluster

We're using Cloudera's CDH3u2 distribution, whose Hue version 1.2.0
requires Python 2.6. Because this is not included in Ubuntu 12.04,
we'll have to use the deadsnakes PPA to install it.
Adding dstat, elinks and colordiff to standard packages; unpinned the activesupport gem as it's better now
fixing node.set complaint in hadoop and hbase; also, ES recipe referring to wrong attribute for cluster name
Elasticsearch tunables:
* flush_threshold is now 'flush_threshold_ops'; the old setting is still used if set.  (NOTE: it wins over the new setting).
* flush_threshold_size and flush_threshold_period to complete the set
* merge_factor -- which controls the segments_per_tier and max_merge_at_once settings -- now chef-defaults to 10 (the ES default is 10)