target_test.py: Use clean paths to avoid failures (#1978)

Currently some tests will fail if you run them twice, because there's no
proper cleanup done.

test/target_test.py

@@ -19,6 +19,7 @@
 from helpers import unittest, skipOnTravis
 from mock import Mock
 import re
+import random
 
 import luigi.target
 import luigi.format
@@ -251,23 +252,25 @@ def test_move_on_fs(self):
         # We're cheating and retrieving the fs from target.
         # TODO: maybe move to "filesystem_test.py" or something
         t = self.create_target()
+        other_path = t.path + '-' + str(random.randint(0, 999999999))
         t._touchz()
         fs = t.fs
         self.assertTrue(t.exists())
-        fs.move(t.path, t.path+"-yay")
+        fs.move(t.path, other_path)
         self.assertFalse(t.exists())
 
     def test_rename_dont_move_on_fs(self):
         # We're cheating and retrieving the fs from target.
         # TODO: maybe move to "filesystem_test.py" or something
         t = self.create_target()
+        other_path = t.path + '-' + str(random.randint(0, 999999999))
         t._touchz()
         fs = t.fs
         self.assertTrue(t.exists())
-        fs.rename_dont_move(t.path, t.path+"-yay")
+        fs.rename_dont_move(t.path, other_path)
         self.assertFalse(t.exists())
         self.assertRaises(luigi.target.FileAlreadyExists,
-                          lambda: fs.rename_dont_move(t.path, t.path+"-yay"))
+                          lambda: fs.rename_dont_move(t.path, other_path))
 
 
 class TemporaryPathTest(unittest.TestCase):