Remove all old logs, not just the zipped up ones.

[edunham]

Fixes #506

The only stuff in these directories is the various logs put there by Buildbot, so we're safe to ditch them.

5 days might be a bit to aggressive but it's what we have before to no major ill effects so I left it. If we want partial logs for a month, it'd be just as easy to run a separate cron job to delete the non-zipped files a bit less enthusiastically.

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This change is 

[edunham]

Travis has failed twice now on assorted intermittents unrelated to this change.

[aneeshusa]

I find that having build history is definitely useful; currently there is ~11GB of history (the disk is 63GB). I would want to keep more than 5 days of history.

Here's some approximate numbers I just looked up:
Other misc files (not logs or bz2 files) (via find /home/servo/buildbot/master -maxdepth 1 -type f | xargs du -sch): 391 MB

Current total bz2 archives (via find /home/servo/buildbot/master -name '*.bz2' -print0 | du -sch --files0-from=-): 4.1Gb

All files without bz2 files (via find /home/servo/buildbot/master -type f -mtime -60 -regextype grep -regex '.*[^b][^z][^2]$' -print0 | du -sch --files0-from=-, changing the number of days):
1 day - 204 MB
2 days - 221 MB
3 days - 235 MB
5 days - 269 MB
15 days - 365 MB
30 days - 486MB
60 days - 698 MB
90 days - 2.3 GB
120 days - 2.5 GB
150 days - 2.7 GB
180 days - 2.8 GB
365 days - 3.7 GB
All time (no logs before 508 days ago) - 6.1 GB

I think if we do get rid of logs, we could probably get away with a 6 month or 1 year cutoff.

[aneeshusa]

I think this will cause an argument too long error, so we'll need to rewrite this differently to not expand all the files in the command line args.

[aneeshusa]

Getting rid of the second /* at the end should probably do the trick. For the bz2 cron, we can add a -name '*.bz2' as well, and make a separate one for all logs.