[Yum] command line server selection

[seth vidal]

> About a month ago, I offered a patch to add support for selecting
> a particular server repository.   Hence avoiding the need to have
> multiple config files, or fiddle about with commenting entries in and out.
> 

> There didn't seem much interest at the time, but I could let
> you have a copy of the patch if you think it would be useful.

It wasn't that there is not any interest, there is just interest in not
creating an option only to remove in the next release b/c the structure
changes.

-sv