filesystem/shared and --default_container_info broken since 1.1

I face this issue, that prevent me to upgrade to 1.1.0 (and the change was consequently introduced in this version):

I'm using default_container_info to mount a /tmp volume in the container's mount namespace from its current sandbox, meaning that each container have a dedicated /tmp, thanks to the filesystem/shared isolator.

I noticed through our automation pipeline that integration tests were failing and found that this is because /tmp (the one from the host!) contents is trashed each time a container is created.

Here is my setup:

• --isolation='cgroups/cpu,cgroups/mem,namespaces/pid,disk/du,filesystem/shared,filesystem/linux,docker/runtime'
• --default_container_info='{"type":"MESOS","volumes":[{"host_path":"tmp","container_path":"/tmp","mode":"RW"}]}'

I discovered this issue in the early days of 1.1 (end of Nov, spoke with someone on Slack), but had unfortunately no time to dig into the symptoms a bit more.

I found nothing interesting even using GLOGv=3.

Maybe it's a bad usage of isolators that trigger this issue ? If it's the case, then at least a documentation update should be done.

Let me know if more information is needed.