Added stout Error and None (w/ tests).

Review: https://reviews.apache.org/r/9304

git-svn-id: https://svn.apache.org/repos/asf/incubator/mesos/trunk@1448464 13f79535-47bb-0310-9956-ffa450edef68
Minor cleanups in src/logging.cpp.

Review: https://reviews.apache.org/r/9305

git-svn-id: https://svn.apache.org/repos/asf/incubator/mesos/trunk@1448465 13f79535-47bb-0310-9956-ffa450edef68
Refactored all Try<T>::error and Result<T>::error to use Error or
ErrnoError (also changed a few CHECKs into CHECK_SOMEs).

Review: https://reviews.apache.org/r/9306

git-svn-id: https://svn.apache.org/repos/asf/incubator/mesos/trunk@1448466 13f79535-47bb-0310-9956-ffa450edef68
Refactored all Option<T>::none and Result<T>::none to use None.

Review: https://reviews.apache.org/r/9307

git-svn-id: https://svn.apache.org/repos/asf/incubator/mesos/trunk@1448467 13f79535-47bb-0310-9956-ffa450edef68