fix(daemon): implement exponential backoff correctly

The exponential backoff code before this was prone to overflow. Instead
of relying on a "try" just increment the interval directly.

This fixes the problem where locksmithd will eat-up a ton of CPU and hit
an infinite loop. I will also cgroup locksmith next.
Merge pull request #14 from philips/fix-cpu-eatup

fix(daemon): implement exponential backoff correctly
fix(daemon): send WaitGroup by reference

The WaitGroup needs to be passed by reference otherwise Done() won't
decrement the WaitGroup that we are actually waiting on.