Fixed coding style issues related to the variable naming convention in stout

Review: https://reviews.apache.org/r/28955
Fixed coding style issues related to the variable naming convention in libprocess

Review: https://reviews.apache.org/r/28956
Fixed coding style issues related to the variable naming convention in the routing library

Review: https://reviews.apache.org/r/28957
Renamed getaddrinfo arguments to be more suggestive

Also add missing call to freeaddrinfo when the call fails

Review: https://reviews.apache.org/r/28958
Introduce process::network namespace.

Introduce process::network namespace to encapsulate socket call wrappers
and Socket class.

Review: https://reviews.apache.org/r/28959