driver: fix yield in fifottl/utubettl

After 1000 processed tuples an iteration fiber yields after each
processed tuple. The problem was fixed by resetting a counter of
processed tuples without yield.

Closes #208

Author: oleg-jukovec

queue/abstract/driver/fifottl.lua

@@ -144,6 +144,7 @@ local function fifottl_fiber_iteration(self, processed)
     if estimated > 0 or processed > 1000 then
         -- free refcounter
         estimated = estimated > 0 and estimated or 0
+        processed = 0
         self.cond:wait(estimated)
     end
 

queue/abstract/driver/utubettl.lua

@@ -152,6 +152,7 @@ local function utubettl_fiber_iteration(self, processed)
         -- free refcounter
         estimated = processed > 1000 and 0 or estimated
         estimated = estimated > 0 and estimated or 0
+        processed = 0
         self.cond:wait(estimated)
     end