{Reviewer: Mike} Add a script to delete old files from /var/log/sprout/ or /var/log/bono ...

...once that directory becomes too large.

Mike, this aims to fix https://github.com/Metaswitch/sprout/issues/121 by deleting the oldest files from /var/log/bono and /var/log/sprout each hour if those directories are too large. It has four separate groups of log files - bono and sprout debug and analysis files - and each group is bounded at 1GB total (which should leave enough space even for an all-in-one node).

I've tested the script manually - by bringing the threshold down to 30KB - and it works, but I haven't tested the package install and cronjob.