User in devel container

[bhack]

We still tell to users to use HOST_PERMS like in https://www.tensorflow.org/install/source#cpu-only_2 but it is used marginally and it doesn't solve permission on your volume mount.

[bhack]

I think we could prefer -u $(id -u):$(id -g) but we need to have a non root user in the image.

[bhack]

Something like:

docker run -it  -w /tensorflow  -v /path_tensorflow_host:/tensorflow -v /path_bazel_cache_host/:/.cache -v $PWD:/mnt  -e USER=tensorflow -u $(id -u):$(id -g) tensorflow/tensorflow:devel bash

it will let to maintain file with you host permission and also to reuse the cache over builds.

[bhack]

With a command like this we could solve tensorflow/tensorflow#39560

[bhack]

Se also my PR at microsoft/vscode-dev-containers#381.

[bhack]

I don't care too much now as we could have user namespaces in rootless mode:
tensorflow/tensorflow#55566