[Merge] ~jbicha/software-properties:no-display into software-properties:ubuntu/master

[Nathan Teodosio]

Update Manager is slow to launch (at least on low-end machines such as 
mine), but Software Properties is probably only very occasionally 
launched by users, so I think this is a good idea.
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https://code.launchpad.net/~jbicha/software-properties/+git/software-properties/+merge/460707
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