launchpad plugin tests should not block landings

[Vincent Ladeuil]

Some tests from the launchpad plugin fail when launchpad is transiently unavailable.

These tests should get plenty of exposure when bzr devs run the full test suite (we all do that several time an hour right ? ;)

If these tests where requiring some feature based on some flag (command-line or say, config option ;) they could be disabled for pqm without losing coverage.

Alternatively we could decorate them so they are retried. Delaying the whole test suite for no more than 5 minutes on pqm won't hurt either.