Fix integration test for file put due to change in pylxd API

This was missed in a previous commit.

Signed-off-by: Alex Kavanagh <alex@ajkavanagh.co.uk>

integration/test_containers.py

@@ -136,10 +136,9 @@ def test_put_get_file(self):
         filepath = '/tmp/an_file'
         data = b'abcdef'
 
+        # raises an exception if this fails.
         retval = self.container.files.put(filepath, data)
 
-        self.assertTrue(retval)
-
         contents = self.container.files.get(filepath)
 
         self.assertEqual(data, contents)