Adjust kernel version parsing to be more lenient of strange things like "3.12-1-amd64"

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
fix divide by zero error

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

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

Docker-DCO-1.1-Signed-off-by: Victor Vieux <victor.vieux@docker.com> (github: vieux)
Merge pull request #4341 from vieux/fix_content_type_copy

fix content-type docker copy
Merge pull request #4328 from vieux/fix_4298

fix divide by zero error
Merge pull request #4316 from tianon/more-lenient-kernel-version

Adjust kernel version parsing to be more lenient of strange things like "3.12-1-amd64"
Merge pull request #4342 from vieux/update_maintainers_api

update api Maintainers file