Fixed 3rdparty stout namespace and todo style

Review: https://reviews.apache.org/r/23598
Fixed 3rdparty libprocess todo and namespace style

Review: https://reviews.apache.org/r/23597
Fixed namespace and todo styles in mesos source

Review: https://reviews.apache.org/r/23596
Enabled todo and namespace rules in style check

Modified cpplint.py to support
} // namespace foo {
  instead of
} // namespace foo

Review: https://reviews.apache.org/r/23599
Fixed lingering namespace style error