systemd: make runlevel work in non-runlevel targets

systemd: make runlevel work in non-runlevel targets

Previously, after booting into the targets like multi-user.target or
graphical.target, the output of `runlevel' command is 'unknown'.

This is confusing for users. Normally, we would expect mutli-user.target
would have a `runlevel' output of 'N 3'.
This is the behaviour of Fedora20.

This patch installs symlinks for systemd-update-utmp-runlevel.service
in do_install task to fix the above problem.

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>