[API] Remove duplicate dependency on "multi_json"
[API] Changed the endpoint for "Nodes Info" API from `/_cluster/nodes` to `/_nodes`

The "_cluster" prefix has been removed in Elasticsearch 1.0.

The "/_nodes" endpoint is supported since ~ version 0.19,
so this doesn't break backwards compatibility.

Related:

* elasticsearch/elasticsearch#4055
* elasticsearch/elasticsearch#4065
* elasticsearch/elasticsearch#4347
* elasticsearch/elasticsearch#4608
[CLIENT] Changed then endpoint from `_cluster/nodes` to `_nodes` when sniffing nodes

Related: elasticsearch-ruby@c408f6c0811d4f1cc3c219522e08e1095186476a
[GEM] Improved unit and integration tests for the "elasticsearch" gem

* Start proper number of nodes, without relying on ENV var
* Mute logger if ENV['QUIET'] is set
* Run exit hooks for integration tests
[CLIENT] Use the `_nodes` endpoint in transport integration tests

Related: baaaba8, 1c81184
[CLIENT] Improved the transport integration tests

* Start proper number of nodes, without relying on the ENV var
[CLIENT] Improved the logging during transport integration tests

* Mute logger when ENV['QUIET'] is set
[EXT] Use the `/_nodes` endpoint in Elasticsearch::Test::Cluster

Related: baaaba8, 1c81184
[EXT] Use the `-f` option in Elasticsearch::Test::Cluster

Because the `es.foreground` setting doesn't actually keep Elasticsearch
in the foreground, and changes the PID, let's use the `-f` option
even though it's not supported on 1.0.

NOTE: Remove the flag in 1.0 version of the gem
[API] Fixed & improved the testing Rake tasks for the API gem

* Fixed incorrectly defined tasks

* Added the code to checkout a specific revision/branch/tag/etc
  during integration tests. Controller either by `build_hash`
  of the running test server, or by the `TEST_BUILD_REF` environment
  variable

Example:

    time QUIET=yes SERVER=start TEST_BUILD_REF=origin/0.90 TEST_CLUSTER_COMMAND=$PWD/tmp/builds/elasticsearch-0.90.10/bin/elasticsearch bundle exec rake test:integration
Improved the main Rakefile
Added `:path` definitions for all the subprojects into main Gemfile
[CI] Improved and update the Travis configuration

* Download Elasticsearch 0.90.10
* Do NOT start test cluster in advance, rely on auto-start with the
  SERVER=yes environment variable