Fix createDirectoryIfMissing to not throw if the dir got deleted

Fix createDirectoryIfMissing to not throw if the dir got deleted
When we call createDirectory and some file system object already exists
we have a problem. We need to distinguish if it is a file that already
exists or if it is a directory because in the latter case it is not an
error. Previously we called doesDirectoryExist however that does not
distinguish the dir not existing (due to another thread deleting it)
and an ordinary file existing. We now use withFileStatus to throw the
original AlreadyExistsError only if a non-directory object exists.
So now the only time we should get a spurious exception is if another
thread deletes the directory and puts a file in its place between our
call to createDirectory and withFileStatus. It should now be safe to
race createDirectoryIfMissing with itself or deleteDirectoryRecursive.