[Merge] ~nteodosio/software-properties:xenial-ua into software-properties:ubuntu/xenial

[Sebastien Bacher]

It works now but any idea why we need the .decode there where it seems it's not in the focal or master versions? Did the python default behavior changed in newer series? if so maybe we should add a code comment explaining?
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https://code.launchpad.net/~nteodosio/software-properties/+git/software-properties/+merge/448388
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