Decode body to array for OpenStack

Hi, im use Selectel (http://storage.selectel.ru) cloud with openstack swift (auth api v1.0), when i try to get_container, im got an error:

```
NoMethodError: undefined method `each' for #<String:0x007ff7aaaf9f98>
	from /Users/bugagazavr/Documents/Ruby/fog/lib/fog/openstack/models/storage/directories.rb:31:in `get'
	from (irb):2
	from /Users/bugagazavr/.rvm/gems/ruby-2.1.0/gems/railties-4.1.0.beta1/lib/rails/commands/console.rb:90:in `start'
	from /Users/bugagazavr/.rvm/gems/ruby-2.1.0/gems/railties-4.1.0.beta1/lib/rails/commands/console.rb:9:in `start'
	from /Users/bugagazavr/.rvm/gems/ruby-2.1.0/gems/railties-4.1.0.beta1/lib/rails/commands/commands_tasks.rb:69:in `console'
	from /Users/bugagazavr/.rvm/gems/ruby-2.1.0/gems/railties-4.1.0.beta1/lib/rails/commands/commands_tasks.rb:40:in `run_command!'
	from /Users/bugagazavr/.rvm/gems/ruby-2.1.0/gems/railties-4.1.0.beta1/lib/rails/commands.rb:17:in `<top (required)>'
	from bin/rails:4:in `require'
	from bin/rails:4:in `<main>'
```

Becouse selectel cloud send me `data.body` as string, not array

```
>> id.directories.get('awesome', :preffix => 'system')
#<Excon::Response:0x007fa8dd463d58
 @body=
  "[{\"hash\": \"b996ceaba5a3f8ba5c18131062380436\", \"last_modified\": \"2014-01-15T18:12:06.865730\", \"bytes\": 295, \"name\": \"system/member/photo/12/test.png\", \"content_type\": \"image/png\"}]",
```

This is a small fix that allows you to convert a string into an array if it is not.