Update various scripts to use the new .format() method

Summary: Avoid using % to format strings, switch to the new method instead.

Test Plan:

./test/functional/test_runner.py wallet_listsinceblock

./test/util/bitcoin-util-test.py

cd share
./qt/extract_strings_qt.py ../src/qt/splashscreen.cpp

Check that a file named qt/bitcoinstrings.cpp is outputted and its
content is correct.

./src/bitcoind -testnet -zmqpubrawtx=tcp://127.0.0.1:28332
-zmqpubrawblock=tcp://127.0.0.1:28332
-zmqpubhashtx=tcp://127.0.0.1:28332
-zmqpubhashblock=tcp://127.0.0.1:28332 &
./contrib/zmq/zmq_sub27.py

Should display a lot of data. Press CTRL+C when you get bored.

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: teamcity, schancel

Differential Revision: https://reviews.bitcoinabc.org/D2577