[COOK-3546] Add: socket connection parameter

http://tickets.opscode.com/browse/COOK-3546

  * Socket can be placed in non-default dir

Usage example:

```ruby
mysql_connection_info = {
  :host => "localhost",
  :username => 'root',
  :password => node['mysql']['server_root_password'],
  :socket => '/db/mysql.sock'
}

mysql_database_user 'newrelic' do
  connection mysql_connection_info
  password newrelic_pass
  action :create
end
```