Tests for CDRIVER-1972 encountered some unexpected behavior of poll in zSeries.

The test introduced a mock poll function. This called the library function poll and sometimes would change the response. The tests would simulate a delayed connection by changing the response of poll to indicate no results. A consequence of this is that poll could be called many more times than it would be in a normal case.

Surprisingly, it seems like because of this mock poll, zSeries would occasionally have large delays (5 or 10 seconds). As a workaround, the timeout passed to poll was reduced to 5ms. We should investigate why this happened, and if there is a better solution.