Fix registry auth by storing the string passed on the command line, and allowing for credential selection by normalizing on hostname. Also, remove remote ping calls from CmdPush and CmdPull.

Docker-DCO-1.1-Signed-off-by: Jake Moshenko <jake@devtable.com> (github: jakedt)
Fix minor typo
handle symlinks for Docker's root dir & TMPDIR

This removes the incomplete symlink handling from engine.go and it adds
it one place in docker.go.

It also enables handling symlinks for TMPDIR.

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
Merge pull request #4437 from SvenDowideit/tweak-DCO-hook-for-windows

Replace `echo -e` with the portable `{ echo; echo ...; }`
Merge pull request #4382 from unclejack/fix_symlink_handling

handle symlinks for Docker's root dir & TMPDIR
Merge pull request #4270 from DevTable/fixregistryauth

Fix registry auth and remove other hidden ping commands from client code
Update daemon docs for exec drivers
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
Merge pull request #4415 from iantruslove/patch-1

Fix minor typo
libcontainer: Use pivot_root instead of chroot

Instead of keeping all the old mounts in the container namespace and
just using subtree as root we pivot_root so that the actual root in
the namespace is the root we want, and then we unmount the previous
mounts.

This has multiple advantages:

* The namespace mount tree is smaller (in the kernel)
* If you break out of the chroot you could previously access the host
  filesystem. Now the host filesystem is fully invisible to the namespace.
* We get rid of all unrelated mounts from the parent namespace, which means
  we don't hog these. This is important if we later switch to MS_PRIVATE instead
  of MS_SLAVE as otherwise these mounts would be impossible to unmount from the
  parent namespace.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
Merge pull request #4438 from crosbymichael/update-docs

Update daemon docs for exec drivers
Add find tests and remove panic in DEBUG
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
Merge pull request #4418 from SvenDowideit/mention-expose-in-port-mapping-deprecation

make the port mapping deprecation error message more obvious
Merge pull request #4448 from alexlarsson/pivot_root

libcontainer: Use pivot_root instead of chroot
Merge pull request #4452 from crosbymichael/small-fixes-to-libcontainer

Add find tests and remove panic in DEBUG
Change veth prefix back to veth

Fixes #4453
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
Merge pull request #4456 from crosbymichael/change-veth-name

Change veth prefix back to veth
Remove loopback mount bind

Docker-DCO-1.1-Signed-off-by: Guillaume J. Charmes <guillaume.charmes@docker.com> (github: creack)
remove /run mountpoint

Docker-DCO-1.1-Signed-off-by: Guillaume J. Charmes <guillaume.charmes@docker.com> (github: creack)
Remove /dev tmpfs mountpoint

Docker-DCO-1.1-Signed-off-by: Guillaume J. Charmes <guillaume.charmes@docker.com> (github: creack)
Merge pull request #4457 from creack/remove_loopback_mount

Remove loopback mount