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)
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)
docker load: add --input flag

for those that do not care to read from redirected stdin

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
docker load: doc clarification

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
docker load: added example of a multiple tag image

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
install.sh (get.docker.io) aufs comment updated.

devicemapper has landed, but the TODO hasn't been actioned presumably
because aufs is still preferred over devicemapper when available[1].

Comment updated accordingly.

Citation [1]: https://github.com/crosbymichael/docker/blob/267ca39921c35826ccbdb84fbbc0690bfef385d7/runtime/graphdriver/driver.go#L40-L46

Docker-DCO-1.1-Signed-off-by: Paul Annesley <paul@annesley.cc> (github: pda)
Merge pull request #4842 from pda/installer-devicemapper-comment

Update AUFS comment in install.sh
Merge pull request #4794 from alexlarsson/dm-better-shutdown

devicemapper: Better/faster shutdown
Merge pull request #4628 from kippandrew/port-allocator

Fix port collision with dynamically allocated ports
Merge pull request #4840 from vbatts/vbatts-load_from_input

docker load: add --input flag