Fix a racy test

Author: behackett

test/test_legacy_api.py

@@ -1160,7 +1160,7 @@ def run(self):
  pass
  coll.ensure_index('foo')
  coll.drop_indexes()
- coll.ensure_index('foo')
+ coll.create_index('foo')
 
  try:
  threads = []