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)
Merge pull request #3566 from tianon/fix-volume-symlinks

Fix symlink mounting issues