Added a Version class to stout.

Currently there is no facility in Mesos for checking compatibility of
various Mesos components that could have been built at different
times with potentially different Mesos versions.  This requirement is
especially important for doing various compatibility checks between
Mesos and Mesos modules (WIP).

Review: https://reviews.apache.org/r/25597
Add docker containerizer destroy tests

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