Fixed authorization tests to properly deal with registration retries.

Review: https://reviews.apache.org/r/25516
Fixed trailing whitespace in libprocess.
Added support for catching trailing white spaces in the style checker.

Review: https://reviews.apache.org/r/25526
Increased session timeouts for ZooKeeper related tests.

- On slower machines sometimes the zookeeper c client times out where we aren't expecting because either the test server or the client is too slow to respond. Increasing this value helps mitigate the problem.

Review: https://reviews.apache.org/r/25487
Pulled the log line in ZooKeeperTestServer::shutdownNetwork() to above the shutdown call.
- When debugging zookeeper related tests it's often more useful to know when the tests is shutting down the ZK server to reason about the order of events. Otherwise client disconnections are often logged before this "shutdown" line and can be confusing.

Review: https://reviews.apache.org/r/25511
Fixed flaky MasterTest.LaunchDuplicateOfferTest.

A couple of races could occur in the "launch tasks on multiple offers"
tests where recovered resources from purposely-failed invocations turned
into a subsequent resource offer and oversaturated the expect's.

Review: https://reviews.apache.org/r/25588
Fixed the flaky FaultToleranceTest.ReconcilePendingTasks.

Review: https://reviews.apache.org/r/25604
Add docker containerizer destroy tests

Review: https://reviews.apache.org/r/24776