Decide to use os.Mkdir when creating chain layer directories since the temporary directory should already exist. The temporary directory is the parent of the chain layer directories, so there is no need to use os.MkdirAll as there will be no intermediate directories.

Decide to use os.Mkdir when creating chain layer directories since the temporary directory should already exist. The temporary directory is the parent of the chain layer directories, so there is no need to use os.MkdirAll as there will be no intermediate directories. #1926