Revert "SERVER-10453 Make DBClientReplicaSet::connect always return true"

This reverts commit 961f3761203d4c1e78f44b898b6bb2cf2b98d00b.

Need to create more tests with slaveok and no primary.
SERVER-10341 disable sync_passive2.js test for 2.5.2 release

We identified a performance regression that prevents this test from finishing
on the Win32 builder and probably any single-core host. We should reenable
the test after the performance regression is addressed.