ovirt-init-functions: validation for systemd-journald

Currently we run service systemd-journald restart on init
for all oVirt Node images. However, we still support distros
which doesn't contain systemd. This patch adds a validation
to execute the systemd-journald only for systemd systems.

Change-Id: I5dc0becfb0b54d4972254ec2a30df15c9f5b480a
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>