Vendor in latest containers/storage and containers/image

Containers/storage brings in support for UserNS ID Mappings
This means we can start experimenting with User NS Support in
podman

Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>

Closes: #596
Approved by: TomSweeneyRedHat

vendor/github.com/containers/storage/drivers/chroot_unix.go

@@ -0,0 +1,21 @@
+// +build linux darwin freebsd solaris
+
+package graphdriver
+
+import (
+	"fmt"
+	"os"
+	"syscall"
+)
+
+// chrootOrChdir() is either a chdir() to the specified path, or a chroot() to the
+// specified path followed by chdir() to the new root directory
+func chrootOrChdir(path string) error {
+	if err := syscall.Chroot(path); err != nil {
+		return fmt.Errorf("error chrooting to %q: %v", path, err)
+	}
+	if err := syscall.Chdir(string(os.PathSeparator)); err != nil {
+		return fmt.Errorf("error changing to %q: %v", path, err)
+	}
+	return nil
+}