EnsureDir errors when target is a broken symlink

[tailhook]

ERROR:vagga::builder: Error building container "tank": step EnsureDir("/var/lock") failed: Error creating dir: File exists (os error 17)
ERROR:vagga::wrapper: Error executing _build: Builder exited with code 1

[tailhook]

Aha, this is because the target is a broken symlink (so it exists, but not a directory)