[Merge] ~ddstreet/software-properties:lp645404 into software-properties:ubuntu/master

[Dan Streetman]

Hold that review for a bit; I'm still working on getting SoftwareProperties out of add-apt-repository.
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https://code.launchpad.net/~ddstreet/software-properties/+git/software-properties/+merge/367276
Your team Ubuntu Core Development Team is requested to review the proposed merge of ~ddstreet/software-properties:lp645404 into software-properties:ubuntu/master.