Execution issue when rootfs is mounted twice "Can't bind mount /oldroot/dev/null on /newroot/dev/null: No such file or directory"

Greetings, sometimes our CI jobs fails when bwrap fails to start and dies with this message: "bwrap: Can't bind mount /oldroot/dev/null on /newroot/dev/null: No such file or directory"

It seems like this happens when the rootfs is mounted twice:
```
$ cat /proc/mounts
rootfs / rootfs rw 0 0
sysfs /sys sysfs rw,seclabel,nosuid,nodev,noexec,relatime 0 0
proc /proc proc rw,nosuid,nodev,noexec,relatime 0 0
devtmpfs /dev devtmpfs rw,seclabel,nosuid,size=3984364k,nr_inodes=996091,mode=755 0 0
securityfs /sys/kernel/security securityfs rw,nosuid,nodev,noexec,relatime 0 0
tmpfs /dev/shm tmpfs rw,seclabel,nosuid,nodev 0 0
devpts /dev/pts devpts rw,seclabel,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=000 0 0
tmpfs /run tmpfs rw,seclabel,nosuid,nodev,mode=755 0 0
tmpfs /sys/fs/cgroup tmpfs ro,seclabel,nosuid,nodev,noexec,mode=755 0 0
cgroup /sys/fs/cgroup/systemd cgroup rw,nosuid,nodev,noexec,relatime,xattr,release_agent=/usr/lib/systemd/systemd-cgrou
ps-agent,name=systemd 0 0
pstore /sys/fs/pstore pstore rw,nosuid,nodev,noexec,relatime 0 0
cgroup /sys/fs/cgroup/blkio cgroup rw,nosuid,nodev,noexec,relatime,blkio 0 0
cgroup /sys/fs/cgroup/net_cls,net_prio cgroup rw,nosuid,nodev,noexec,relatime,net_prio,net_cls 0 0
cgroup /sys/fs/cgroup/cpuset cgroup rw,nosuid,nodev,noexec,relatime,cpuset 0 0
cgroup /sys/fs/cgroup/perf_event cgroup rw,nosuid,nodev,noexec,relatime,perf_event 0 0
cgroup /sys/fs/cgroup/devices cgroup rw,nosuid,nodev,noexec,relatime,devices 0 0
cgroup /sys/fs/cgroup/cpu,cpuacct cgroup rw,nosuid,nodev,noexec,relatime,cpuacct,cpu 0 0
cgroup /sys/fs/cgroup/freezer cgroup rw,nosuid,nodev,noexec,relatime,freezer 0 0
cgroup /sys/fs/cgroup/hugetlb cgroup rw,nosuid,nodev,noexec,relatime,hugetlb 0 0
cgroup /sys/fs/cgroup/memory cgroup rw,nosuid,nodev,noexec,relatime,memory 0 0
cgroup /sys/fs/cgroup/pids cgroup rw,nosuid,nodev,noexec,relatime,pids 0 0
configfs /sys/kernel/config configfs rw,relatime 0 0
/dev/vda1 / xfs rw,seclabel,relatime,attr2,inode64,noquota 0 0
rpc_pipefs /var/lib/nfs/rpc_pipefs rpc_pipefs rw,relatime 0 0
selinuxfs /sys/fs/selinux selinuxfs rw,relatime 0 0
systemd-1 /proc/sys/fs/binfmt_misc autofs rw,relatime,fd=28,pgrp=1,timeout=0,minproto=5,maxproto=5,direct,pipe_ino=1302
8 0 0
debugfs /sys/kernel/debug debugfs rw,relatime 0 0
mqueue /dev/mqueue mqueue rw,seclabel,relatime 0 0
hugetlbfs /dev/hugepages hugetlbfs rw,seclabel,relatime 0 0
nfsd /proc/fs/nfsd nfsd rw,relatime 0 0
tmpfs /run/user/0 tmpfs rw,seclabel,nosuid,nodev,relatime,size=801012k,mode=700 0 0
/dev/vda1 / xfs rw,seclabel,relatime,attr2,inode64,noquota 0 0

$ bwrap --dir /tmp --tmpfs /tmp --chdir /tmp/ --dir /var --dir /var/tmp --dir /run/user/974 --ro-bind /usr /usr --ro-bind /lib /lib --ro-bind /lib64 /lib64 --ro-bind /bin /bin --ro-bind /sbin /sbin --ro-bind /etc/resolv.conf /etc/resolv.conf --ro-bind /etc/hosts /etc/hosts --proc /proc --dev /dev --unshare-all --share-net --die-with-parent /bin/echo ok
bwrap: Can't bind mount /oldroot/dev/null on /newroot/dev/null: No such file or directory
```

I'm still looking for how this double "/dev/vda1 / xfs" mount happens... This is an OpenStack cloud instance and perhaps the cloud-init growroot process does the remount? There is also a service that bind mount / to /srv/host-rootfs to run runC containers that may be causing the double mount.

It seems like an expected behavior as the bwrap initial pivot_root may not have the SLAVE flag on the right mount point or something... Any help to debug this would be appreciated :-)