add options for rrdcached timeout and delay values

This adds options to the template for rrdcached's run script to control timeout (how often to write rrds) and delay (random splay for individual rrds) as well as default attributes with values equal to the currently hardcoded values.

The existing behavior writes out rrds within 5min of receiving them, while I have configured my systems to write out every 30s for real-time-y looking graphs.  Different patterns of collection and IO bandwidth will benefit from wildly different values for these config options.