prevent warning of cloning existing resources and call yum makecache on a per repo basis

When using the ```key``` and then the ```repository``` LWRP using the name of the key resource to define the key attribute implicitly, the repository LWRP will create (clone) the key resource resulting in a warn log message for CHEF-3694. 
The same warning will also appear if you define multiple repository resources with each resource calling the ```yum-makecache``` execute  and the ```reload-internal-yum-cache```  ruby-block resource.

To prevent this i suffixed the resources with the name of the repo.

The second commit will change the behaviour of the ```yum-makecache``` resource to get the metadata only for the current repository. In case of multiple repositories this is a lot faster.