Fix symlink mounting issues by evaluating symlinks directly on the LHS of a bind-mount -v and by FollowSymlinkInScope on the RHS just before mounting

Tested successfully with variations around mounting /var/run and /var/run/docker.sock inside a "debian" container directly at /var/run/docker.sock where /var/run is a symlink to "/run" on both the host and in the container.

Fixes #3262

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
docs: simplify basic usage doc, step 1: check your docker install

docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)
docs: move a sysadmin-focused topic out of the basic usage manual and into installation docs (setting up a user group for non-root access)

docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)
docs: add standard 'check your docker install' paragraph to the 'hello world' examples.

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)
docs: "first steps with docker" is a better title than "learn basic commands"

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)
Docs: move advanced topic "create your own base image" out of basic user guide

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)
Docs: fix capitalization of "Docker"

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)
Merge pull request #3566 from tianon/fix-volume-symlinks

Fix symlink mounting issues
Merge pull request #3688 from shykes/docs-simplify-basic-usage

Simplify basic usage docs
Move docker rmi to a job

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
remove buffer

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)