docker exec should use working directory of container image by default

[hickeng]

Story
As a user of VCH containers I expect consistent behaviour with regular docker.

Detail
docker exec was updated to use the container image working directory as part of the shift to containerd (see moby/moby@ddae20c#diff-3ed197c0a6f7a9ca73a3ee424e448ac1R222).

We should adopt this behaviour for consistency with base docker, but should do so at the same time as adding support for the exec -w option to explicitly set the working directory so that there is an easy path for restoring old behaviour.

This is not target at a patch release as it's a breaking behaviour.

Workaround
It's not a great workaround, but it's the same approach as was needed before docker changed the behaviour:

sh -c "cd /desired/dir && command-to-run"

[stuclem]

Added the following to the release notes:

• docker exec should use working directory of container image by default . #8166
  docker exec was updated to use the container image working directory as part of the shift to containerd. vSphere Integrated Containers does not yet implement the exec -w option, so does not behave consistently with Docker.

  Workaround: Use the same approach as was necessary before Docker changed the behavior:

  sh -c "cd /desired/dir && command-to-run

@hickeng does this cover it?

[stuclem]

Already in the RNs. Removing note tag.