Update contrib/devtools scripts to use the new .format() method

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

Test Plan:

./contrib/devtools/copyright_header.py report src
./contrib/devtools/copyright_header.py update src
./contrib/devtools/copyright_header.py insert src/addrman.cpp

Check that there is no error and that a new copyright notice is
correctly added at the beginning of src/addrman.cpp

./contrib/devtools/security-check.py build/src/bitcoind

Should return no error

./contrib/devtools/security-check.py src/addrman.cpp

Should return src/addrman.cpp: unknown format

./contrib/devtools/symbol-check.py build/src/bitcoind

May output a lot of things, but throw no exception

./contrib/devtools/update-translations.py

May output a lot of things, but throw no exception

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: teamcity, schancel

Differential Revision: https://reviews.bitcoinabc.org/D2575