Add support for RandomSleep option

[frankatwork]

Add option to change the RandomSleep option in 10periodic

[daenney]

A few things:

• Can we move away from "NONE" in favour of undef? It would allow you to go randomsleep.nil? in the template to check if it is set. I know dl_limit uses "NONE" too but I'd rather not add any more code that does that;
• randomsleep is not being validated, no validate_ functions are being called to check the input;
• You add a test to check for the behaviour if randomsleep is set, but you don't have a test for the NONE/undef scenario;
• It should be squashed into one commit before we merge.

[daenney]

This commit hasn't received any attention for two months, I'm going to close it for now. Feel free to reopen it once rebased and the issues have been addressed.