shadow: add 'util-linux-sulogin' to RDEPENDS

shadow: add 'util-linux-sulogin' to RDEPENDS

If shadow is installed, sulogin from busybox cannot work correctly because
it still assumes that /etc/shadow is not there. This leads to the problem
when booting into rescue mode in an image with shadow installed but not
sulogin from util-linux.

To fix this problem, we add 'util-linux-sulogin' to RDEPENDS of shadow.
This runtime dependency is specific to OE, because we have to ensure
that sulogin can work correctly and sulogin from busybox cannot because
FEATURE_SHADOWPASSWORDS is not enabled by default. And we cannot enable
it by default for busybox, because that would lead to utilities in busybox
to assume the existence of /etc/shadow which is not always true in OE.

[YOCTO #6698]

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>