Recommend different location for yum.conf in mock

[Jeff Pitman]

Hi:

When dealing with building yum itself inside of a mock chroot, it's 
better to do this:

        yumconf = os.path.join(self.rootdir, 'etc', 'yum.repos.d', 
'mock.conf')

Instead of messing with rpmsave/rpmnew.

-- 
-jeff