libcontainerd has a bunch of platform dependent code and huge interfaces
that are a pain implement.
To make the plugin manager a bit easier to work with, extract the plugin
executor into an interface and move the containerd implementation to a
separate package.
Signed-off-by: Brian Goff <cpuguy83@gmail.com>
Upstream-commit: c85e8622a4813d7b72d74517faa03ab5de4c4550
Component: engine
