Updated stout to satisfy whitespace/line_length.

Review: https://reviews.apache.org/r/20976
Fix typo in slave/flags.hpp regarding --recovery=cleanup mode.
Updated ReviewBot to look at old reviews first.

Review: https://reviews.apache.org/r/20617
Add a return statement to Varint64Comparator::Compare in leveldb to
silence the compiler warning. This patch fixes this build error with
ICC.

Review: https://reviews.apache.org/r/21292
Moved ReconcileTaskTest test to its own file.

Review: https://reviews.apache.org/r/21175
Fixed tasks reconciliation and added tests.

Review: https://reviews.apache.org/r/21236
Fixed white space in authorizer.hpp
Added slave operation counters to Master.

Review: https://reviews.apache.org/r/21290
Allowed Gauge to take synchronous functions.

Review: https://reviews.apache.org/r/20995
Added --override flag to command executor.

It will be a common use case that external containerizer programs will
have to be able to control the command being carried out when the only
the task.command or container image is present.  The command executor
will in its current state try to run the command in the context of the
slave and not the container.

So, you could imagine the command executor being used by: 1) Replace
the command to run when the slave sends a runTask message 2) Prefix a
command to wrap call in when the slave sends a runTask message.

1) have been implemented and tested in this patch, alongside making
the command-executor "cli-ized" with help messages.

Review: https://reviews.apache.org/r/21329
Updated 'containers' implementation to forward to the ECP.

Updates 'containers' implementation within the ExternalContainerizer
to forward the call to the ECP.  Adds new 'containers' proto message
to containers.proto.

Some minor cleanups like removing of needless namespace mentions that
slipped through.

NOTE: The test_containerizer.py implementation of 'containers' is
incomplete, it merely poses as a mock-up.  NOTE: This does *not* fix
MESOS-1257. A complete test_containerizer C++ implementation is
upcoming to fix these notes.

Review: https://reviews.apache.org/r/21040
Enriched the Java Docs in ZooKeeperState.java.

Review: https://reviews.apache.org/r/21085
Updated 'recover' implementation to forward to the ECP.

Review: https://reviews.apache.org/r/21130
Revert "Allowed Gauge to take synchronous functions."

Bug: MESOS-1286

This reverts commit 249011b3d71fcc1776104132391c2011335788d5.
Added test for killing unknown task with Slaves in transitional state.

Review: https://reviews.apache.org/r/21249
Updated CHANGELOG for 0.18.2-rc1.
Introduced '--' to flags parsing.

Review: https://reviews.apache.org/r/21384
Added override of Flags::load that updates 'argc' and 'argv'.

Review: https://reviews.apache.org/r/21388
Added task gauges to slave metrics.

Review: https://reviews.apache.org/r/21276
Added support for passing flags in override command.

Calling the mesos executor with "./mesos-executor --override ./foo
--bar" would cause the executor flags parsing to fail as it would
continue evaluating arguments as potential flags candidates.  r21388
and r21384 adds the option to use a "--" terminator, which will cause
the mesos flag parsing to stop and modify argv to contain the
remaining arguments.

Review: https://reviews.apache.org/r/21408