[Merge] ~alexmurray/ubuntu-dev-tools:fix-ppa-pull-lp-1938659 into ubuntu-dev-tools:master

[Mattia Rizzolo]

perhaps you can use `yield from` instead of the loop?  Also, is the same change needed in the private ppa cases visible in the same hunk?

Lastly, if changes are going to be needed, please include the bug reference (either LP:# or url) in the commit message.
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https://code.launchpad.net/~alexmurray/ubuntu-dev-tools/+git/ubuntu-dev-tools/+merge/406518
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