On Python 3, rarfile<3.0 does not support bytes filename
### Problem

Importing  rar files does not work anymore. It used to work with beets `1.4.2` and below.

The underlying problem is that `is_rarfile` does no accept bytes (and `toppath` variable is byte). See this commit https://github.com/markokr/rarfile/commit/7d7a2cbf04cf4572c26e38ba18b5fe0b049cd850 where future versions (once or twice a year) of `rarfile` will gladly accepts bytes.

Running this command in verbose (`-vv`) mode:

```sh
beet -vv import /mnt/E/Album\\ -\\ group.rar
```

Led to this problem:

```
user configuration: /home/lompik/.config/beets/config.yaml
data directory: /home/lompik/.config/beets
plugin paths: 
Sending event: pluginload
library database: /home/lompik/.data/musiklibrary.blb
library directory: /mnt/music
Sending event: library_opened
Sending event: import_begin
Extracting archive: /mnt/E/Album - group.rar
extraction failed: Invalid object passed as file
No files imported from /mnt/E/Album - group.rar
Sending event: import
Sending event: cli_exit
```



### Setup

* OS: Linux
* Python version: 3.6
* beets version: 1.4.3  / rafile version: 3.0
* Turning off plugins made problem go away (yes/no): no


EDIT: change filename
diff --git a/beets/importer.py b/beets/importer.py
index bbe152cd4..690a499ff 100644
--- a/beets/importer.py
+++ b/beets/importer.py
@@ -988,7 +988,7 @@ class ArchiveImportTask(SentinelImportTask):
         `toppath` to that directory.
         """
         for path_test, handler_class in self.handlers():
-            if path_test(self.toppath):
+            if path_test(util.py3_path(self.toppath)):
                 break
 
         try:
['beets/importer.py']