Automatically clean out data/txn files after failures

[vvolkl]

Originally https://its.cern.ch/jira/browse/CVM-1462

For a long time the StratumOnes twiki has recommended that stratum 1s clean out old files from the /srv/cvmfs//data/txn directories, but I just learned that release manager machines can suffer the same problems of old files accumulating there after failed publish operations. I think cvmfs_swissknife or cvmfs_server could do a better job of cleaning those out after any type of failure, on both stratum 1s and release managers. There used to be a concern of one operation interfering with another, but now we have locks and if the cleanup is done before the lock is released there should be no danger of that.

[DrDaveD]

Are you sure that the issue was on a release manager? The report that prompted this issue was in this forum thread. Maybe it is only gateways. Release managers themselves don't have the txn directories as far as I can see.

For reference, here's the instructions on the StratumOnes twiki and here's the instructions in the OSG stratum1 instructions. It should probably at least be in the cvmfs readthedocs stratum 1 maintence section.