Merge pull request #7094 from fredlf/update_docker-hub

New screenshots and a few small edits.
Skip whole dir dockerignoring with warning

Fixes #7093
Docker-DCO-1.1-Signed-off-by: Alexandr Morozov <lk4d4math@gmail.com> (github: LK4D4)
Updated Red Hat Enterprise Linux installation instructions for version 7

Docker-DCO-1.1-Signed-off-by: Brian Exelbierd <bex@pobox.com> (github: bcexelbi)
Move `docker ps` test to integration cli

Docker-DCO-1.1-Signed-off-by: Fabio Falci <fabiofalci@gmail.com> (github: fabiofalci)
Update docs on --sig-proxy to indicate that SIGKILL and SIGSTOP cannot be proxied

Docker-DCO-1.1-Signed-off-by: Matt Heon <mheon@redhat.com> (github: mheon)
Merge pull request #6984 from jameskyle/6937-allow-setting-of-docker-config-directory

Closes 6937. Allows setting of docker config dir.
Improve data volume container example.
Docker-DCO-1.1-Signed-off-by: Jason Livesay <ithkuil@gmail.com> (github: runvnc)
Add logout command

"docker logout [SERVER]" will remove the registry server' credentials from
.dockercfg file. If a server is not specified, it will log user out of the
default docker registry server

Docker-DCO-1.1-Signed-off-by: Daniel, Dao Quang Minh <dqminh89@gmail.com> (github: dqminh)
fix doc references

Docker-DCO-1.1-Signed-off-by: Daniel, Dao Quang Minh <dqminh89@gmail.com> (github: dqminh)
Tests on container state changing

It could catch error that was fixed in #6954
Docker-DCO-1.1-Signed-off-by: Alexandr Morozov <lk4d4math@gmail.com> (github: LK4D4)
update style

Docker-DCO-1.1-Signed-off-by: Victor Vieux <vieux@docker.com> (github: vieux)
Merge pull request #7079 from LK4D4/state_tests

Tests on container state changing
Merge pull request #7069 from crosbymichael/update-libcontainer-july3

Update libcontainer to be85764f109c3f0f62cd2a5c8be
Merge pull request #7077 from tianon/fix-ubuntu-systemd

Fix hack/make/ubuntu to install both docker.service and docker.socket
Merge pull request #7106 from vieux/logout

Add logout command
Update runmetrics.md
Merge pull request #7098 from fabiofalci/move_ps_tests_to_cli

Move `docker ps` test to integration cli
Merge pull request #6933 from ztombol/feat-mkimage-arch-expect

Fix expect script in mkimage-arch
Update libcontainer to cf45d141db69ce11dcccac178e5

Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@docker.com> (github: crosbymichael)
Merge pull request #7107 from bkochendorfer/patch-1

Update runmetrics.md