Echonest conversion command: only use byte strings

Temp file name was unicode, so if other parts of the command were
utf8-encoded non-ascii strings the command would fail (in
beets.util.command_output()). Requesting a temp file with a byte string
path fixes the issue.

Fix #1407.

beetsplug/echonest.py

@@ -289,7 +289,7 @@ class EchonestMetadataPlugin(plugins.BeetsPlugin):
         pending.
         This is stolen from Jakob Schnitzers convert plugin.
         """
-        fd, dest = tempfile.mkstemp(u'.ogg')
+        fd, dest = tempfile.mkstemp(b'.ogg')
         os.close(fd)
 
         self._log.info(u'encoding {0} to {1}',

test/test_echonest.py

@@ -109,6 +109,12 @@ class EchonestCliTest(unittest.TestCase, TestHelper):
         self.assertNotEqual(item.path,
                             echonest_track.call_args[1]['filename'])
 
+    @patch('pyechonest.song.search')
+    @patch('beetsplug.echonest.CONVERT_COMMAND', 'cp $source $dest')
+    def test_analyze_convert2(self, echonest_search):
+        self.add_item(format='FLAC', path=b'm\xc3\xacn.flac')
+        self.run_command('echonest')
+
     @patch('pyechonest.song.profile')
     @patch('pyechonest.song.search')
     @patch('pyechonest.track.track_from_filename')