yum Damaged repomd.xml file

It is not a damage of your repomd.xml (repository meta data). I see here two possible problems:

• your proxy server has a stale partially retrieved copy or just refuses to give a good one.
• The bad copy was put onto the repository master server and then all mirrors pull it (I used to see it). Anyway at time I write the response the first picked mirror returned a valid file.

Your fedora.repo file is fine.

I got it working by adding a proxy tag in my yum.conf file which was initially missing.