Publishing results from inside a Linux Docker container fails

pytest-azurepipelines uses /proc/1/mountinfo to translate the result file path
to the host path before broadcasting. But mountinfo will only deliver the
path relative to the mount point on the host, e.g. when the data disk is mounted to
/data on the host and the workspace is in /data/agents/...
Inside the container mountinfo will show /agents/... mounted to __w/....
The translation will pick the wrong base path and the result upload will fail.
It would be helpful to have a command line option or environment variable
to pass the root of the host mount to pytest. When given the prefix should be
considered in path translation.

Start by tracing the /proc/1/mountinfo path translation and result-upload flow described in the issue. Determine how a host-mount root supplied through a command-line option or environment variable should affect translation; done means publishing from the Linux Docker container resolves the host path and uploads results successfully.

Written by the indexing model from the issue text.