Support hairpin NAT without going through docker server

Hairpin NAT is currently done by passing through the docker server.  If
two containers on the same box try to access each other through exposed
ports and using the host IP the current iptables rules will not match the
DNAT and thus the traffic goes to 'docker -d'

This change drops the restriction that DNAT traffic must not originate
from docker0.  It should be safe to drop this restriction because the
DOCKER chain is already gated by jumps that check for the destination
address to be a local address.

Docker-DCO-1.1-Signed-off-by: Darren Shepherd <darren.s.shepherd@gmail.com> (github: ibuildthecloud)
Resync the DCO text with upstream at http://developercertificate.org/

```
Everyone is permitted to copy and distribute verbatim copies of this
license document, but changing it is not allowed.
```

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Prevent dynamic allocation of previously allocated ports

Docker-DCO-1.1-Signed-off-by: Andy Kipp <andy@rstudio.com> (github: kippandrew)
Better test error message

Docker-DCO-1.1-Signed-off-by: Andy Kipp <andy@rstudio.com> (github: kippandrew)
Be more explicit in finding next port to allocate

Docker-DCO-1.1-Signed-off-by: Andy Kipp <andy@rstudio.com> (github: kippandrew)
Add err checks for port allocator tests

Docker-DCO-1.1-Signed-off-by: Andy Kipp <andy@rstudio.com> (github: kippandrew)
libcontainer/network: add netns strategy

Docker-DCO-1.1-Signed-off-by: Johan Euphrosine <proppy@google.com> (github: proppy)
libcontainer/nsinit/init: move mount namespace after network

Docker-DCO-1.1-Signed-off-by: Johan Euphrosine <proppy@google.com> (github: proppy)
libcontainer: goimports

Docker-DCO-1.1-Signed-off-by: Johan Euphrosine <proppy@google.com> (github: proppy)
libcontainer: remove duplicate imports

Docker-DCO-1.1-Signed-off-by: Johan Euphrosine <proppy@google.com> (github: proppy)
docker save: --output flag

for those that do not care to redirect stdout

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
docker save: add and improve docs

add usage examples for `docker save ...`

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
Remove duplication of Dns in config merging.

Fixes #4714
Docker-DCO-1.1-Signed-off-by: Alexandr Morozov <lk4d4math@gmail.com> (github: LK4D4)
api/client: var style tweak

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
fix failing test to use kill instead of stop

TestCreateStartRestartStopStartKillRm was failing because stop has been
changed to not kill containers.

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
Harmonize / across all name-related commands

Docker-DCO-1.1-Signed-off-by: Djibril Koné <kone.djibril@gmail.com> (github: enokd)

Harmonize / across all name-related commands

Docker-DCO-1.1-Signed-off-by: Djibril Koné <kone.djibril@gmail.com> (github: enokd)

Harmonize / across all name-related commands:Return an error when repeated /

Docker-DCO-1.1-Signed-off-by: Djibril Koné <kone.djibril@gmail.com> (github: enokd)
I'm not looking forward to documenting cli arguments that may or may not show depending on what plugins / drviers you choose

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@fosiki.com> (github: SvenDowideit)
Merge pull request #4782 from unclejack/fix_TestCreateStartRestartStopStartKillRm

fix failing test to use kill instead of stop
devicemapper: Better/faster shutdown

Right now shutdown is looping over *all* devicemapper
devices and actively deactivating them, this is pretty
slow if you have a lot of non-active containers. We
instead only deactivate the devices that are mounted.

We also do the shutdown unmount using MNT_DETACH which
forces the unmount in the global namespace, even if it
is busy because of some container having it mounted.
This means the device will be freed when that container
exits.

Also, we move the call to waitClose to deactivateDevice
because all callers of any of them call both anyway.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
Fix double single dash arg issues in docs

Docker-DCO-1.1-Signed-off-by: Brian Goff <cpuguy83@gmail.com> (github: cpuguy83)