Reverted "Upgraded ZooKeeper from 3.3.4 to 3.3.6.".

This reverts commit eb1cd4a7c0ad4310f090d4f0643cf4059ac5246b.
Reverted "Added resource checks to slave recovery tests to ensure
resources are re-offered after restarts."

This reverts commit 400a88f9817bb102522b08b83dca400380ad8a9b.
Fixed os::chdir return value checking in launcher.cpp.

From: Vinson Lee <vlee@freedesktop.org>
Review: https://reviews.apache.org/r/13880
Fixed clang mismatched-tags errors in process.cpp.

From: Vinson Lee <vlee@freedesktop.org>
Review: https://reviews.apache.org/r/13879
Fixed clang return-type build error in os::sendfile.

From: Vinson Lee <vlee@freedesktop.org>
Review: https://reviews.apache.org/r/13840