Change the way cron run times are calculated

Make the puppet run interval more configurable by allowing to modify it
by changing a single value instead of a value + a cron entry. The ERB
calculates the cron entry now using the interval and crontimes values.
An assumption is made that the maximum interval is 60 minutes and the
minimum 1 minute.
Forthermore enable splay for puppet runs allowing hosts to delay up to
45s their runs. This allows for a better distribution of puppet runs in
a minute resulting in a more balanced load on the puppetmasters
Finally make the freshness interval dependable on the interval (albeit
somewhat hardcoded) and have icinga complain about freshness checks
stating the time the service is a failed state avoiding the need to
change the freshness check interval in multiple places

Change-Id: Ie44b37f45a2962954927e988947315e8d9459400