Changes calcuation of variable delay

In the loopingcall.FixedIntervalLoopingCall class, an warning is logged
when 'delay' is equal or less than zero. Commonly delayed time is
considered something over due from a deadline which is a positive value.

Also a task delayed zero seconds is not considered delayed
but finished on time.

Therefore this patch fixes the calculation of the variable 'delay' and
omits a warning log when 'delay' is zero

Change-Id: I9dbae0838e6c03fa0eaa79e7332e650b02ed9c77
Merge "Changes calcuation of variable delay"