Use GeoIP sites from CVMFS, if possible

[bbockelm]

Right now, we hardcode the endpoints for the possible GeoIP services in the code. We should switch that to using attr -qg host_list /cvmfs/oasis.opensciencegrid.org as suggested in the code.

If that fails, it's OK to use the hardcoded list. Some sites (such as those exporting via NFSv3) may not have this feature available.

[djw8605]

So, are you ok with adding a dependency on xattr python module? Otherwise, I would have to run this command with popen, or whatever. Is attr built into a base EL6/EL7 install?

[bbockelm]

I think you'd have to check on EL6, but yum requires pyxattr on EL7. So, there's a good possibility that it is available. It appears libattr (which is needed by pyxattr) is a dependency for coreutils, so that's probably pretty globally available.

You'll need to work with Suchandra on this though - we need to decide whether stashcp should use python from CVMFS or the system.

Regardless - you can probably have the following sequence:

1. If xattr module is available, then use that.
2. Else, popen the attr command line utility.
3. Else, use the hardcoded server list. As with caches.json, can we move the server list out of python and into a hardcoded file? Maybe just put this in caches.json itself?