Revert "Make sure the mesos-fetcher exits if the slave terminates."

This reverts commit f66fa52e7efd9c10f9256805e45095591d4833a7.
Added some slave recovery DockerContainerizer tests.

Review: https://reviews.apache.org/r/24765
Set ownership of stdout/stderr and container directory properly.

Review: https://reviews.apache.org/r/24766
Validate Docker version since we require >= 1.0.0.

Review: https://reviews.apache.org/r/24767
Save Docker container pid for subsequent containerizer updates.

Review: https://reviews.apache.org/r/24768