Ensure that check for the interrupt is done on every getNext() call in datasize_kill_op.js

BF-25019 encountered a case where even though the command is marked as killed, it returns the success code, as while executing no check for the interrupt is being made.

In order to force this check, we set the number of iterations allowed prior the check to be performed to be 1. Meaning that on every getNext() call, the check will be made.