fix systemd import-tar for gentoo

use a newer version of systemd
Fixes https://review.openstack.org/#/c/608102

Change-Id: I23fd671adb893f3abd9fbc65382f2aec5a317c24

diskimage_builder/elements/gentoo/pre-install.d/02-gentoo-02-flags

@@ -30,6 +30,11 @@ echo 'sys-boot/grub device-mapper' >> /etc/portage/package.use/grub
 # needed in order to install pip packages as root
 echo '=dev-python/pip-9.0.1-r2 ~amd64' >> /etc/portage/package.keywords/pip
 
+if [[ "${GENTOO_PROFILE}" == *"systemd"* ]]; then
+    # systemd import-tar is broken, use a more recent (fixed) version
+    echo '~sys-apps/systemd-241 ~amd64' >> /etc/portage/package.keywords/systemd
+fi
+
 if [[ "${GENTOO_PROFILE}" == *"musl"* ]]; then
     echo "dev-vcs/git -gpg" >> /etc/portage/package.use/musl  # gpg doesn't build on musl profiles
     echo "=sys-block/open-iscsi-2.0.874-r1 ~amd64" >> /etc/portage/package.keywords/musl