[Merge] lp:~jamesodhunt/upstart/cleanup-test-xdg-dirs into lp:upstart

[Dmitrijs Ledkovs]

previously we didn't unset DBUS_SYSTEM_BUS_ADDRESS anywhere, and at the moment the tests don't spawn their own system dbus. maybe it's best to leave it available in the environment?
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https://code.launchpad.net/~jamesodhunt/upstart/cleanup-test-xdg-dirs/+merge/194848
Your team Upstart Reviewers is requested to review the proposed merge of lp:~jamesodhunt/upstart/cleanup-test-xdg-dirs into lp:upstart.