RepositorySet-API: Added the functionality to enable RedHat Repos.

Added `list_rhproducts` function to list all the RedHat Products
in a given Organization.

RH Products have varying Id's depending upon various other custom
products, hence we use the product-label which is a static value
to fetch the RH Product's ID in `fetch_rhproduct_id` function.

RH Reposets too have varying ID's hence we use reposet-label which
is a static value to fetch the RH Reposet's ID in `fetch_reposet_id`
functio.

Also RH Repositories first need to be enabled , so that they can be
synced.
`enable_repo` and `disable_repo` functions requires the
`reposet_id`, `basearch` and `releasever` to enable, disable the
repositories.
> I don't know what to say, if you don't believe.

Show me a unit test.

> Also I cannot right the test, for this as per the existing format of the tests, as the path needs to be constructed depending upon the reposetid.

An entity does not need to exist to make a path for that entity. For example:

```
Python 2.7.8 (default, Jul  1 2014, 17:30:21) 
[GCC 4.9.0 20140604 (prerelease)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from robottelo import entities
>>> entities.Repository().path()
'https://example.com/katello/api/v2/repositories'
>>> entities.Repository(id=5).path()
'https://example.com/katello/api/v2/repositories/5'
>>>
```