Return NotFound error for cgroups abs paths

Signed-off-by: Michael Crosby <michael@docker.com>
Change not found error to be typed with cgroup subsystem

Signed-off-by: Michael Crosby <michael@docker.com>
Ignore not found erros in Paths

Signed-off-by: Michael Crosby <michael@docker.com>
Merge pull request #161 from crosbymichael/return-notfound-err

Return NotFound error for cgroups abs paths
Added support for Libseccomp syscall filtering

Vendored golang-seccomp bindings for libseccomp added, as is a build dependency
on libseccomp version 2.1 or higher.

Signed-off-by: Matthew Heon <mheon@redhat.com>