Move runtime implementation types to pkg

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

runtime.go

@@ -1,9 +0,0 @@
-package containerd
-
-import "github.com/opencontainers/specs"
-
-// runtime handles containers, containers handle their own actions.
-type Runtime interface {
-	Create(id, bundlePath string, stdio *Stdio) (Container, error)
-	StartProcess(Container, specs.Process, *Stdio) (Process, error)
-}