[FIX] Updated the "rubygems_db_master" Chef role

* Removed hardcoded addresses, added defaults for Vagrant-based deployments (eg. `33.33.33.10` as the address)
* Added missing default "postgres" user
* Added listening on all addresses by default
* Changed database name to "rubygems_staging" to reflect the current setup naming
Allow deploying a specific `revision` of the application in the "rails" recipe

Used eg. to deploy a different branch then master.
[SEARCH] Added configuration for Elasticsearch nodes

This commit adds support for search nodes running Elasticsearch.

* The "elasticsearch" cookbook [https://github.com/elasticsearch/cookbook-elasticsearch/]
  has been added to the Cheffile

* A Vagrant VM named `search` has been added

* A `search` role has been added

* Node configurations (*.json) for Vagrant and EC2 have been added

* The Capistrano tasks have been updated to reflect the changes

To deploy in EC2:

    # Update packages
    #
    RUBYGEMS_EC2_SEARCH=abc-123.compute-1.amazonaws.com \
    DEPLOY_USER=ubuntu \
    DEPLOY_SSH_KEY=~/.ssh/mykey.pem \
      cap rubygems.org invoke COMMAND='sudo apt-get update' SUDO=true

    # Install Chef
    #
    RUBYGEMS_EC2_SEARCH=abc-123.compute-1.amazonaws.com \
    DEPLOY_USER=ubuntu \
    DEPLOY_SSH_KEY=~/.ssh/mykey.pem \
      cap rubygems.org invoke COMMAND='curl -# -L http://www.opscode.com/chef/install.sh | sudo bash -s --' SUDO=true

    # Run Chef
    #
    time \
    RUBYGEMS_EC2_SEARCH=abc-123.compute-1.amazonaws.com \
    DEPLOY_USER=ubuntu \
    DEPLOY_SSH_KEY=~/.ssh/mykey.pem \
      cap rubygems.org chef:search

Related: rubygems/rubygems.org#455
[SEARCH] Added a template for Elasticsearch application initializer

The `elasticsearch_url` variable is set in the "secret/rubygems" data bag,
similar to setting PostgreSQL host, etc.

Alternatively, an environment variable `ELASTICSEARCH_URL` could be used.

Related: rubygems/rubygems.org#455
Update highline dependency to version 1.6.19
Merge pull request #122 from karmi/search

Added Elasticsearch integration
Fixed up database settings
Fixed up disk for ES
Put datadog into alphabetical order
Use XFS everywhere and manage the proper device
Remove tire config generation
Remove broken automation code from ES
Fix the search domain [rubygem.org -> rubygems.org]
Adding marpaia to the users databag
Merge pull request #124 from marpaia/master

Adding marpaia to the users databag
Update mixlib-shellout dependency to version 1.2.0
Update ohai dependency to version 6.18.0
Update treetop dependency to version 1.4.14
Update mime-types dependency to version 1.24
Update treetop dependency to version 1.4.15