Bind mount /proc/ in container contains hostOS information

[alexgg]

When the supervisor mount the /proc filesystem into a container it justs bind mounts the host's /proc into the container. This is wrong as it will expose incorrect information like PIDs from the hostOS that are invalid in the container and might confuse some applications.

A workaround is for the container to instead mount a new /proc filesystem but it requires CAP_SYS_ADMIN capabilities to mount:

$ mount none -t procfs /proc

Relates-to: https://balena.zendesk.com/agent/tickets/2728

[pipex]

This is a good point, we might need to deprecate this label at some point.