Fix duplicate iptables rules

If iptables version is < 1.4.11, try to delete the rule vs. checking if it exists. Fixes #6831.

Docker-DCO-1.1-Signed-off-by: Jessica Frazelle <jfrazelle@users.noreply.github.com> (github: jfrazelle)
use correct apt-key for test.docker.io/ubuntu

Docker-DCO-1.1-Signed-off-by: Jessica Frazelle <jess@docker.com> (github: jfrazelle)
Document how to pass ENV vars to the user's shell

As this is a somewhat common question.

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@docker.com> (github: SvenDowideit)
Allow /etc/hosts and /etc/resolv.conf to be updated both outside and
inside the container.

Docker-DCO-1.1-Signed-off-by: Erik Hollensbe <github@hollensbe.org> (github: erikh)
Append instead of replace file contents

I think the `DOCKER_OPTS` should be appended to `/etc/default/docker` and not replace the entire contents.
The default name of the bridge created is called 'docker0'.
docs: shrink images

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
docs: change kernel version requirement

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
clean up the context when a build fails

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
Merge pull request #8038 from unclejack/failed_build_context_cleanup

clean up the context when a build fails
Adding Exec method to native execdriver.
Modified Attach() method to support docker exec.

Docker-DCO-1.1-Signed-off-by: Vishnu Kannan <vishnuk@google.com> (github: vishh)
Adding support for docker exec in daemon.

Docker-DCO-1.1-Signed-off-by: Vishnu Kannan <vishnuk@google.com> (github: vishh)
Adding 'exec' command to remote API and CLI.

Docker-DCO-1.1-Signed-off-by: Vishnu Kannan <vishnuk@google.com> (github: vishh)
Import nsenter in docker.

Docker-DCO-1.1-Signed-off-by: Vishnu Kannan <vishnuk@google.com> (github: vishh)
Fix bug in attach handling for docker exec. Add docs for 'docker exec' feature.

Docker-DCO-1.1-Signed-off-by: Vishnu Kannan <vishnuk@google.com> (github: vishh)
Update cli.md to include 'docker exec' feature.
Docker-DCO-1.1-Signed-off-by: Vishnu Kannan <vishnuk@google.com> (github: vishh)
Adding integration tests for docker exec feature.

Docker-DCO-1.1-Signed-off-by: Vishnu Kannan <vishnuk@google.com> (github: vishh)
Address review comments.

Docker-DCO-1.1-Signed-off-by: Vishnu Kannan <vishnuk@google.com> (github: vishh)
Removing 'exec' feature from the CLI until the docker daemon supports resizing of
tty sessions for exec'ed commands.

Docker-DCO-1.1-Signed-off-by: Vishnu Kannan <vishnuk@google.com> (github: vishh)
Change the copy command Content-Type header to x-tar
Addresses #6107

Signed-off-by: Srini Brahmaroutu <srbrahma@us.ibm.com>