Frequent cleanup of Buildbot logs

[mloskot]

This task is about adding script and cronjob that will periodically clean log files in all Buildbot instances. This should help us to avoid run out of disk space on xblade14-2.

[mloskot]

The cleaner script has ben created and it lives here

/osgeo/buildbot/buildbot_clean_logs.sh

The cleaner brings off following steps for Buildbot instance of every project:

1. Stop Buildbot instance for project
2. Visit project buildmaster
3. Clean logs of each builder of the project
4. Clean changes log
5. Clean buildbot log
6. Get out of project buildmaster
7. Start Buildbot instance after cleanup

Manual execution:

cd /osgeo/buildbot
./buildbot_clean_logs.sh

I've not configured cronjob yet. I will try to run cleanup script 1-2 times manually to see that it works well and then I'll configure cronjob.

[warmerdam]

We have lots of space so this isn't pressing, and the log cleanup is well documented in the wiki.