Add support for environment-specific run lists to Role and Role.Builder

The Role and Role.Builder classes in the org.jclouds.chef.domain package don't provide methods for manipulating environment-specific run list entries.

The JSON representation of a Role that includes environment-specific run lists looks like this:

{
  "name": "jclouds-role",
  "description": "",
  "json_class": "Chef::Role",
  "default_attributes": {

  },
  "override_attributes": {

  },
  "chef_type": "role",
  "run_list": [

  ],
  "env_run_lists": {
    "env1": [
      "recipe[env1.alpha]",
      "recipe[env1.bravo]"
    ],
    "env2": [
      "recipe[env2.alpha]",
      "recipe[env2.bravo]"
    ]
  }
}

To address this gap, I suggest the following changes:

1. The constructor for org.jclouds.chef.domain.Role needs to include a parameter that contains the environment run list.
2. The org.jclouds.chef.domain.Role should include a getter for the environment run list.
3. The org.jclouds.chef.domain.Role.Builder class should include a method for adding an entry to the environment run list.

I plan to prepare a pull request that will include these changes.