CI: add tests in cgroupv2

.umlrootfs/Dockerfile

@@ -0,0 +1,13 @@
+FROM debian:buster
+RUN apt-get update && apt-get install -y systemd rsh-redone-server ifupdown sudo kmod
+RUN echo "host" > /root/.rhosts && \
+    chmod 600 /root/.rhosts && \
+    /bin/echo -e "auto eth0\niface eth0 inet static\naddress 254.255.255.2/24" > /etc/network/interfaces.d/eth0 && \
+    sed -i '/pam_securetty/d' /etc/pam.d/rlogin && \
+    cp /usr/share/systemd/tmp.mount  /etc/systemd/system && \
+    systemctl enable tmp.mount
+
+RUN echo "deb http://deb.debian.org/debian experimental main" >> /etc/apt/sources.list && \
+    apt-get update && \
+    apt-get install -y make && \
+    apt-get install -y -t experimental cgroup-tools