Add a script to check all the metalink urls

[ralphbean]

We had some metalink doom over the last couple days and a couple things were painful:

• Rebuilding the umdl took forever (6-8 hours?). The script in First pass at update-single-file-detail #93 was added to try and make that much faster when we know what's wrong.
• Checking that all the metalinks actually work after we rebuilt and synced out the pickle. We have to manually ssh around to f22, f21, f20, epel, etc, boxes and try to 'yum update' for both updates and updates-testing. It would be excellent if we had a script that just tried to download the metalink and validate it (somehow). We could then easily loop over all the metalinks and verify them from one box. We could do this automatically from nagios.

[adrianreber]

@puiterwijk should we include your metalink checker into the mirrormanager2 repository?

[pypingou]

@puiterwijk thoughts?

[pypingou]

@puiterwijk ?

[ralphbean]

Ping @puiterwijk - can you add details here?