Deployqt script: Stylistic changes

Pylint recommendations
- filter -> list comprehension
- whitespace fixes
- unused import
- unused variable
- variable overriding builtin
- missing exception types

Also simplify copy-ignore-helper

Change-Id: Ibf7c573af35d60937f23a85d7a52e20031f38c4b
Reviewed-by: Kai Koehne <kai.koehne@theqtcompany.com>