tree-wide: use f-strings

[d4nuu8]

This series of patches replaces all "old-school" string formatting by f-strings.

This "fixes" all (668) pylint messages "consider-using-f-string / C0209".

See https://pylint.pycqa.org/en/latest/user_guide/messages/convention/consider-using-f-string.html

This improves pylint's rating from 8.73 to 9.28 out of 10.

[d4nuu8]

@bgermann As requested on the mailing list.

I still need to check the problems you are having building a initvm with this applied.

[d4nuu8]

Changes since last version:

• Fix f-string in elbepack/commands/init.py
• Add two more f-strings to elbepack/repodir.py

diff.txt

@bgermann initvm creation and build are working now.

[d4nuu8]

@bgermann May I ask for any feedback here?

[bgermann]

This will take time because I have to manually verify this manual approach.

[bgermann]

Integrated. Thanks for the contribution!