[Merge] lp:~abompard/postorius/mockingmmclient into lp:postorius

Aurélien Bompard has proposed merging lp:~abompard/postorius/mockingmmclient into lp:postorius. Requested reviews: Mailman Coders (mailman-coders) For more details, see: https://code.launchpad.net/~abompard/postorius/mockingmmclient/+merge/242186 This branch makes use of the new mailmanclient mocking class (which must be merged first). (I also removed a few unused imports) -- Your team Mailman Coders is requested to review the proposed merge of lp:~abompard/postorius/mockingmmclient into lp:postorius.