Updated the "fog" gem in "elasticsearch::ebs" recipe to 1.21.0

I had some errors when running the cookbook as, it turned out, I didn't set the AWS region correctly.
Fog (version 1.12.1) returns a null instance for aws when the region is incorrect with no verbose debug information when this occurs:

    NoMethodError: ruby_block[Create EBS volume on /dev/sda2 (size: 25GB)] (elasticsearch::ebs line 16) had an error: NoMethodError: undefined method `volumes' for nil:NilClass
    /var/chef-solo/cookbooks/elasticsearch/libraries/create_ebs.rb:41:in `block (2 levels) in create_ebs'

Instead with the latest version it was able to show the issue more explicitly:

    ArgumentError
    -------------
    Unknown region: "us-west-2b"

Closes #200
Changed `AWS_ACCESS_KEY` variable name to `AWS_ACCESS_KEY_ID` in the Rakefile
Pinned "faraday" dependency for "ridley" to 0.8.9

Prevent error:

    /opt/chef/embedded/lib/ruby/gems/1.9.1/gems/faraday-0.9.0/lib/faraday.rb:99:in `method_missing': undefined method
    `register_middleware' for #<Faraday::Connection:0x000000035e5b48> (NoMethodError)

Related: RiotGames/ridley#239, RallySoftware-cookbooks/cookbook-development@a92d3b9
Added the `skip_start` attribute

Sometimes we may not want elasticsearch to start right after an installation.

Closes #201
Revert "Fixed the "maxBackupIndex" support"

This reverts commit e65d06f7388185fe26647413bfac41757746a7a4.
Revert "Added the `maxBackupIndex` option to the default log appender"

This reverts commit 7661969159ffecfd4a904a943cf250bcc4e49d6e.
Release 0.3.8
Allow any custom configuration