Allow docker containers to be scheduled for removal
Fix docker flaky tests

Conflicts:
	src/slave/containerizer/docker.cpp
Add priviledged option to docker info
Support lxc configurations in docker containerizer
Add docker hostname option.
Symlink sandbox directories in docker containerizer

Review: https://reviews.apache.org/r/26517
Avoid docker inspect on each usage call

Review: https://reviews.apache.org/r/26436