Update restrict.Restrict to both show the error message when failing to mount /dev/null over /proc/kcore, and to ignore "not exists" errors while doing so (for when CONFIG_PROC_KCORE=n in the kernel)

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Fixed typo in docs - intro - working with docker - working with images.  It read that you can use both images used by others and images used by others, in a run-on sentence.
Merge pull request #5673 from tianon/kcore-error

Update restrict.Restrict to both show the error message when failing to mount /dev/null over /proc/kcore, and to ignore "not exists" errors while doing so (for when CONFIG_PROC_KCORE=n in the kernel)
devmapper: Remove accidental debug spew

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
Merge pull request #5680 from alexlarsson/dm-remove-spew

devmapper: Remove accidental debug spew
Merge pull request #5679 from tdaws/master

Fixed typo in docs - intro - working with docker - working with images. ...