use correct apt-key for test.docker.io/ubuntu

Docker-DCO-1.1-Signed-off-by: Jessica Frazelle <jess@docker.com> (github: jfrazelle)
Merge pull request #8001 from jfrazelle/fix-key-for-test-release-ubuntu

use correct apt-key for test.docker.io/ubuntu
It seems that we need these 2 options enabled for both aufs and devicemapper drivers when running on EXT4 - so test for them

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@docker.com> (github: SvenDowideit)
hack/install.sh: install apparmor when enabled

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
Merge pull request #8080 from SvenDowideit/test-for-ext4-fs-kernel-options

It seems that we need these 2 options enabled for both aufs and devicema...
Merge pull request #8083 from unclejack/install_apparmor

hack/install.sh: install apparmor when enabled
Add "hack/install.sh" to the "PRs welcome" note in the end of the install script

Also, simplified the output method by using `cat >&2 <<EOF ...` instead of multiple lines of `echo >&2 '...'`.

Signed-off-by: Andrew Page <admwiggin@gmail.com>
move stdcopy to pkg/stdcopy

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
stdcopy: improve perf by avoiding buffer growth

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
Benchmark for StdWriter.Write

Signed-off-by: Alexandr Morozov <lk4d4@docker.com>
Merge pull request #6 from LK4D4/benchmark_for_8084

Benchmark for StdWriter.Write
Merge pull request #8085 from tianon/hack-install-location

Add "hack/install.sh" to the "PRs welcome" note in the end of the install script
Merge pull request #8084 from unclejack/improve_stdcopy

stdwriter: improve perf by avoiding buffer growth