Fix exponential backof bug

[alonf]

A bug in the Exponential back of utility is that the exponent part is always seconds, even when we use minutes.
We need to fix and ensure that we add 1,2,4... minutes and not second:
Change this:
var exponentialDelay = Math.Pow(2, retryCount) + initialDelay.TotalSeconds / unitOfTime(1).TotalSeconds;

to something like:

var exponentialDelay = unitOfTime(Math.Pow(2, retryCount)) + initialDelay.TotalSeconds / unitOfTime(1).TotalSeconds;

Validate that this is the correct approach