Fixed mounting with containerized kubelet.

Kubelet was not able to mount volumes when running inside a container and
using nsenter mounter,

NsenterMounter.IsLikelyNotMountPoint() should return ErrNotExist when the
checked directory does not exists as the regular mounted does this and
some volume plugins depend on this behavior.

pkg/util/mount/mount.go

@@ -34,6 +34,7 @@ type Interface interface {
 	// consistent.
 	List() ([]MountPoint, error)
 	// IsLikelyNotMountPoint determines if a directory is a mountpoint.
+	// It should return ErrNotExist when the directory does not exist.
 	IsLikelyNotMountPoint(file string) (bool, error)
 }
 

pkg/util/mount/nsenter_mount.go

@@ -170,6 +170,12 @@ func (n *NsenterMounter) IsLikelyNotMountPoint(file string) (bool, error) {
 		return true, err
 	}
 
+	// Check the directory exists
+	if _, err = os.Stat(file); os.IsNotExist(err) {
+		glog.V(5).Infof("findmnt: directory %s does not exist", file)
+		return true, err
+	}
+
 	args := []string{"--mount=/rootfs/proc/1/ns/mnt", "--", n.absHostPath("findmnt"), "-o", "target", "--noheadings", "--target", file}
 	glog.V(5).Infof("findmnt command: %v %v", nsenterPath, args)