Clean up imports to be pyflakes-checkable. fixes #2450

Signed-off-by: Daira Hopwood <daira@jacaranda.org>

qa/rpc-tests/walletbackup.py

@@ -34,9 +34,16 @@ and confirm again balances are correct.
 """
 
 from test_framework.test_framework import BitcoinTestFramework
-from test_framework.util import *
+from test_framework.util import assert_equal, initialize_chain_clean, \
+    start_nodes, start_node, connect_nodes, stop_node, \
+    sync_blocks, sync_mempools
+
+import os
+import shutil
 from random import randint
+from decimal import Decimal
 import logging
+
 logging.basicConfig(format='%(levelname)s:%(message)s', level=logging.INFO)
 
 class WalletBackupTest(BitcoinTestFramework):