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>
Prettify docs-update.py

Remove commented code, use format for string concatenation, split long lines, fix how-to-run instructions
Signed-off-by: Davide Ceretti <dav.ceretti@gmail.com>
Edits and fixes to Dockerfile Best Practices based on review feedback.

Docker-DCO-1.1-Signed-off-by: Fred Lifton <fred.lifton@docker.com> (github: fredlf)
Create registry_api_client_libraries.md
Signed-off-by: Konrad Kleine <konrad.wilhelm.kleine@gmail.com>
Add registry_api_client_libraries.md to mkdocs.yml

Signed-off-by: Konrad Kleine <konrad.wilhelm.kleine@gmail.com>
Update host_integration.md
Add ENV variables support to WORKDIR build command

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
Docker-DCO-1.1-Signed-off-by: Adrien Folie <folie.adrien@gmail.com> (github: folieadrien)

Conflicts:
	builder/builder.go
		This file has been deleted.
registry: getting Endpoint ironned out

Signed-off-by: Vincent Batts <vbatts@redhat.com>
Update libtrust version

Updated to version of libtrust with the trust graph implementation

Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)
fix help message for mkimage debootstrap with components

debootstrap needs the suite as the second argument, for this the script
reorders arguments beginning with a minus but components separated by
space, as stated by the help message, is not handled and will lead to
the rootfs being passed as suite to debootstrap.
The poor mans solution is to fix the help message to pass the long
option as one argument.

Signed-off-by: Julian Taylor <jtaylor.debian@googlemail.com>
Merge pull request #8337 from tjwebb123/patch-1

Update host_integration.md
Add erikh as maintainer of pkg/proxy

Docker-DCO-1.1-Signed-off-by: Erik Hollensbe <github@hollensbe.org> (github: erikh)
Merge pull request #8350 from erikh/add_erikh_maintainer_proxy

Add erikh as maintainer of pkg/proxy
Print a status message when pull command is executed
Using repo tag in the status message for better usability, as per review comments
Added documentation and Changed code to print Status after downloads are complete

Addresses #2404

Signed-off-by: Srini Brahmaroutu <srbrahma@us.ibm.com>
Merge pull request #8346 from juliantaylor/mkimage-debootstrap

fix help message for mkimage debootstrap with components
Fixed issue with docs not getting built due to ssl error.
Signed-off-by: Ken Cochrane <ken@docker.com>
Add provenance pull flow for official images

Add support for pulling signed images from a version 2 registry.
Only official images within the library namespace will be pull from the
new registry and check the build signature.

Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)
Typo: changed "Maintainers" to "maintainers"

Signed-off-by: Konrad Kleine <konrad.wilhelm.kleine@gmail.com>