Discard all data on devicemapper devices when deleting them

This works around the fact that deleting a device in a thin pool
doesn't discard the free space. Unfortunately even this is not perfect,
as it seems discards are respected only for blocks that has never been
shared in the thin device code. However, this has been fixed in the
upstream kernel device-mapper tree:

http://git.kernel.org/cgit/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=for-next&id=0ab1c92ff748b745c1ed7cde31bb37ad2c5f901a

When this hits the kernel I belive this will fully return space
for removed images/containers to the host FS. For now it only
helps partially (which is better than nothing).

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
Fixes 3497
Docker-DCO-1.1-Signed-off-by: Andy Rothfusz <github@developersupport.net> (github: @metalivedev)
Fix odd issues with "make docs", add "make docs-shell", and canonicalize our docs Dockerfile a bit more

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Fix release.sh sed of install.sh so we preserve tests against 'https://get.docker.io/'

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
fix doc, load and get

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
Merge pull request #3593 from dotcloud/fix_doc

fix doc, load and get
Merge pull request #3598 from tianon/fix-vieux-docs-errors-again

Fix odd issues with "make docs", add "make docs-shell", and canonicalize...
move viz to a job

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
update TODO

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
Merge pull request #3613 from vieux/deprecated_viz_job

move viz to a job
move copy to a job

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
Merge pull request #3560 from vieux/copy_job

move copy to a job
move insert to a job

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
use the same 'Used' method as before

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
Merge pull request #3559 from vieux/insert_job

move insert to a job
fix docker insert display

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
Merge pull request #3617 from dotcloud/fix_insert_display

fix docker insert display
move attach to a job

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
Merge pull request #3512 from vieux/attach_job

move attach to a job
move search to a job

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)