systemd: cleanup /var/run on boot and create /var/run/utmp

* Angstrom uses /var/run cleanup because:
  Some apps (e.g. avahi-daemon) to clean up their old-style pid files and fail
  to start every other boot. Se we let systemd clean it on boot.
  Which seems general enough, so lets move var-run.conf from base-files.bbappend
  to systemd recipe.

* /var/run/utmp was created by volatiles before, but without sysvinit installed
  systemd-update-utmp-runlevel.service fails to start without this file

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>