Only unshare the mount namespace for execin

Fixes #4728
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)
Merge pull request #4731 from crosbymichael/fix-execin

Only unshare the mount namespace for execin
add env hint

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@fosiki.com> (github: SvenDowideit)
devmapper: Increase timeout in waitClose to 10sec

As reported in https://github.com/dotcloud/docker/issues/4389 we're
currently seeing timeouts in waitClose on some systems. We already
bumped the timeout in waitRemove() in
https://github.com/dotcloud/docker/issues/4504.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
Merge pull request #4738 from SvenDowideit/mention-env-scrubbing

add env hint
Merge pull request #4739 from alexlarsson/dm-timeout

devmapper: Increase timeout in waitClose to 10sec
Merge pull request #4674 from vbatts/vbatts-graphdriver_build_tags

graphdriver: build tags
btrfs: build tags

Default to the same build behavior, but allow a go build tag to disable
building of the btrfs graphdriver

	go build -tags no_btrfs' ...
	$ go build
	$ objdump -S docker | grep btrfs | wc -l
	194
	$ go build -tags no_btrfs
	$ objdump -S docker | grep btrfs | wc -l
	1
	# that is a comment ;-)

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
btrfs: build tags

correct filename and make the tag more readable

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
packagers: btrfs build tag docs

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

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