Add DeleteProcess API for removing execs

We need a separate API for handing the exit status and deletion of
Exec'd processes to make sure they are properly cleaned up within the
shim and daemon.

Fixes #973

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

cmd/ctr/exec.go

@@ -63,7 +63,7 @@ var execCommand = cli.Command{
 		if err != nil {
 			return err
 		}
-		defer process.Delete()
+		defer process.Delete(ctx)
 
 		statusC := make(chan uint32, 1)
 		go func() {

cmd/ctr/shim.go

@@ -10,7 +10,6 @@ import (
 	"log"
 	"net"
 	"os"
-	"strconv"
 	"time"
 
 	gocontext "context"
@@ -154,13 +153,7 @@ var shimDeleteCommand = cli.Command{
 		if err != nil {
 			return err
 		}
-		pid, err := strconv.Atoi(context.Args().First())
-		if err != nil {
-			return err
-		}
-		r, err := service.Delete(gocontext.Background(), &shim.DeleteRequest{
-			Pid: uint32(pid),
-		})
+		r, err := service.Delete(gocontext.Background(), &shim.DeleteRequest{})
 		if err != nil {
 			return err
 		}