fix super in tests for py27

beembase/objects.py

beembase/operations.py

beemgraphenebase/operations.py

tests/test_account.py

tests/test_aes.py

tests/test_amount.py

tests/test_asset.py

tests/test_base_objects.py

tests/test_comment.py

tests/test_market.py

tests/test_message.py

tests/test_objectcache.py

tests/test_steem.py

tests/test_txbuffers.py

tests/test_wallet.py