Use logical time for batch timeout.

[Yoav Tock]

Currently the batcher uses

timeout := time.After(b.batchTimeout)

for timeout, need to use logical time or the task scheduler that uses logical time.

[yacovm]

I can reason why we can use a function that mocks time, like to mock time.After or something but I'm not sure we need to use the task scheduler in the production code.

We never test in integration tests anything that has to do with batch timeout, and we always use small timeouts anyway.