improve docs for Gentoo Linux installation

Changes summary:
    * Added available USE flags table(description included).
    * Added some tips regarding the use of docker in the Gentoo environment.
    * Sorted out docker installation ways.
    * Added information about the newly created Gentoo Docker team.
    * Misc improvements

Signed-off-by: Pavlos Ratis <dastergon@gentoo.org>
Add more info about when build cache is invalidated/used - Issue #3636
Plus some edits as suggested by @jamtur01

Closes #3636

Signed-off-by: Doug Davis <dug@us.ibm.com>
Update libcontainer to c744f6470e37be5ce1f1ae09b84

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>
Merge pull request #8210 from dastergon/improve_gentoodoc

improve docs for Gentoo Linux installation
Update native driver to set RootFs

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>
Source the bash_completion after installation

Signed-off-by: Przemek Hejman <przemyslaw.hejman@gmail.com>
Merge pull request #8289 from duglin/FixTestcaseFor8230

Fixes the new testcase for PR #8230
Strongly type exec driver context

This also removes dead code in the native driver for a past feature that
was never fully implemented.

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>
Adding self to various maintainers files.

Docker-DCO-1.1-Signed-off-by: Jessica Frazelle <jess@docker.com> (github: jfrazelle)
Merge pull request #8112 from dmcgowan/libtrust_key_management

Libtrust key management
Fixed simple typo

Signed-off-by: Scott Collier <emailscottcollier@gmail.com>
Merge pull request #8295 from crosbymichael/type-exec-context

Strongly type exec driver context
Add --security-opts options to allow user to customize security configuration

security-opts will allow you to customise the security subsystem.

For example the labeling system like SELinux will run on a container.

    --security-opt="label:user:USER"   : Set the label user for the container
    --security-opt="label:role:ROLE"   : Set the label role for the container
    --security-opt="label:type:TYPE"   : Set the label type for the container
    --security-opt="label:level:LEVEL" : Set the label level for the container
    --security-opt="label:disabled"    : Turn off label confinement for the container

Since we are passing a list of string options instead of a space separated
string of options, I will change function calls to use InitLabels instead of
GenLabels.  Genlabels interface is Depracated.

Docker-DCO-1.1-Signed-off-by: Dan Walsh <dwalsh@redhat.com> (github: rhatdan)
Merge pull request #8293 from crosbymichael/update-libcontainer-sep8

Update libcontainer to c744f6470e37be5ce1f1ae09b842c15c1bee120d
add apparmor:

Signed-off-by: Victor Vieux <vieux@docker.com>
Merge pull request #8296 from scollier/typo

Fixed simple typo
Doc update to clarify EXPOSE vs -p functionality.

Signed-off-by: Daniel Farrell <dfarrell@redhat.com>
Merge pull request #8280 from duglin/Issue3636

Add more info about when build cache is invalidated/used - Issue #3636
Merge pull request #8281 from dfarrell07/master

Doc update to clarify EXPOSE vs -p functionality.
Filter containers by status.

A continuation of #7616.
Adds `docker ps --filter=status=(restarting|running|paused|stopped)` option.

Docker-DCO-1.1-Signed-off-by: Jessica Frazelle <jess@docker.com> (github: jfrazelle)