add --releasever=/ to mkimage-yum.sh

I didn't realize the commit required a Docker-DCO so it failed the travis-ci build. So I removed the commit from my forked repo. Now it looks like there is a pull request with no commit. So here it is again:

Needed to add '--releasever=/' flag to run yum groupinstall on Centos7 (didn't try on anything else). This snippet from yum man page explains why:

```
Note: You may also want to use the option --releasever=/ when creating the installroot as otherwise the $releasever value is taken from the rpmdb within the installroot (and thus.  will  be  empty,  before  creation).
```

Docker-DCO-1.1-Signed-off-by: Matt Schurenko <matt.schurenko@gmail.com> (github: mschurenko)
devmapper: include dm_deps information in debug

Signed-off-by: Vincent Batts <vbatts@redhat.com>
daemon logging: unifying output and timestamps

A little refactor of the ./pkg/log so engine can have a logger instance

Signed-off-by: Vincent Batts <vbatts@redhat.com>
Adding self to various maintainers files.

Docker-DCO-1.1-Signed-off-by: Jessica Frazelle <jess@docker.com> (github: jfrazelle)
Implementing IPv6 functionality for ipallocator

Closes #6975

Signed-off-by: Malte Janduda <mail@janduda.net>
Add more names

Docker-DCO-1.1-Signed-off-by: Brian Goff <bgoff@cpuguy83-mbp.home> (github: cpuguy83)
pkg/version: lint and add comments
docker save: Do not save to a terminal.

Docker-DCO-1.1-Signed-off-by: Erik Hollensbe <github@hollensbe.org> (github: erikh)
pkg/truncindex: lint and add comments

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
pkg/units: lint

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
pkg/timeutils: lint and add comments

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
registry: lint

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
pkg/graphdb: some linting

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
Fix the bug of tag a existed tag name of a repository.

Signed-off-by: Lei Jitang <leijitang@huawei.com>
reflect changes introduced in d2ffcd9 in docs

Docker-DCO-1.1-Signed-off-by: Brice Jaglin <bjaglin@teads.tv> (github: bjaglin)
on truncated output, show canonical name rather than first name

Docker-DCO-1.1-Signed-off-by: Brice Jaglin <bjaglin@teads.tv> (github: bjaglin)
Import ps name parsing for default name

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>
Add some docs about which env vars are defined in new containers

@SvenDowideit FYI

Closes #3087

Signed-off-by: Doug Davis <dug@us.ibm.com>
Make V2 code more defensive against malformed content

Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)
Use direct registry url

Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)