Add the python extension to the macdeployqtplus script
This is a python script, so let's call it like a python script.
This causes the script to be parsed by all the python linters, so this
diff updates it accordingly. This is a lot of changes but it's
arc lint -- contrib/macdeploy/macdeployqtplus.py ninja osx-dmg
Reviewers: #bitcoin_abc, deadalnix
Reviewed By: #bitcoin_abc, deadalnix
Differential Revision: https://reviews.bitcoinabc.org/D7969