skeleton: make /run a proper directory/filesystem

Making /var/run and /run symlinks to /tmp is bad since the underlying
tmpfs filesystem is mode 1777 which leads to possible security attack
vectors via badly owned/mask-mode pidfiles and state files residing there.

So make /run a proper directory with /var/run symlinked to it.
Eventually all startup scripts and state info should be pointed to /run
directly as per the linux fhs and good practice.

Add a tmpfs filesystem entry for /run so that busybox inittab, systemv
inittab and systemd automount mounts it there to avoid breaking the
system.

While at it fix inconsistent spacing in /etc/fstab by using tabs and
drop the "static file system information" header whatever that means.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>