[qa] py2: Unfiddle strings into bytes explicitly

Github-Pull: #7853
Rebased-From: faa41ee204, fa7abe0a00

 Conflicts:
	qa/rpc-tests/invalidtxrequest.py
	qa/rpc-tests/p2p-feefilter.py
	qa/rpc-tests/proxy_test.py
	qa/rpc-tests/test_framework/mininode.py
	qa/rpc-tests/test_framework/netutil.py
	src/test/bctest.py

src/test/bctest.py

@@ -2,6 +2,7 @@
 # Distributed under the MIT software license, see the accompanying
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
+from __future__ import division,print_function,unicode_literals
 import subprocess
 import os
 import json