Fix `test_import_dir`

[daavoo]

test_import_dir fails because of how FakeHadoopFS resolves the path in:

https://github.com/iterative/dvc-hdfs/blob/7186552907ac516bcbf02d2bacc3d9b74294e8b8/dvc_hdfs/tests/fixtures.py#L204-L216

Originally posted by @daavoo in #1 (review)