cgroup bindmounts are not correct without a cgroupfs mount entry

[cyphar]

If the config.json is missing a cgroup mount entry (in a rootless container for example), the cgroup mounts are still present but are not correct:

bash-4.3# grep cgroup /proc/self/mountinfo
242 240 0:22 / /sys/fs/cgroup ro,nosuid,nodev,noexec - tmpfs tmpfs ro,mode=755
243 242 0:23 / /sys/fs/cgroup/unified rw,nosuid,nodev,noexec,relatime - cgroup2 cgroup rw
244 242 0:24 / /sys/fs/cgroup/systemd rw,nosuid,nodev,noexec,relatime - cgroup cgroup rw,xattr,name=systemd
245 242 0:26 / /sys/fs/cgroup/rdma rw,nosuid,nodev,noexec,relatime - cgroup cgroup rw,rdma
246 242 0:27 / /sys/fs/cgroup/hugetlb rw,nosuid,nodev,noexec,relatime - cgroup cgroup rw,hugetlb
247 242 0:28 / /sys/fs/cgroup/net_cls,net_prio rw,nosuid,nodev,noexec,relatime - cgroup cgroup rw,net_cls,net_prio
248 242 0:29 / /sys/fs/cgroup/cpu,cpuacct rw,nosuid,nodev,noexec,relatime - cgroup cgroup rw,cpu,cpuacct
249 242 0:30 / /sys/fs/cgroup/memory rw,nosuid,nodev,noexec,relatime - cgroup cgroup rw,memory
250 242 0:31 / /sys/fs/cgroup/blkio rw,nosuid,nodev,noexec,relatime - cgroup cgroup rw,blkio
251 242 0:32 / /sys/fs/cgroup/cpuset rw,nosuid,nodev,noexec,relatime - cgroup cgroup rw,cpuset
252 242 0:33 / /sys/fs/cgroup/perf_event rw,nosuid,nodev,noexec,relatime - cgroup cgroup rw,perf_event
253 242 0:34 / /sys/fs/cgroup/pids rw,nosuid,nodev,noexec,relatime - cgroup cgroup rw,pids
254 242 0:35 / /sys/fs/cgroup/devices rw,nosuid,nodev,noexec,relatime - cgroup cgroup rw,devices
255 242 0:36 / /sys/fs/cgroup/freezer rw,nosuid,nodev,noexec,relatime - cgroup cgroup rw,freezer

[cyphar]

I found this while testing #1540.