[MERGE] Bulk update all test adaptation into a single approach, using multiply_tests rather than test adapters.

[Vincent Ladeuil]

>>>>> "robert" == Robert Collins <robert.collins at canonical.com> writes:

    robert> This overhauls our test parameterisation to be consistent throughout
    robert> bzrlib, gets rid of some cases of scanning for tests multiple times
    robert> (which should make loading test suite faster, though I haven't measured
    robert> this specifically).

    robert> I did this to make sure that the helpers we'd been evolving really did
    robert> work for all of bzrlib, and to get rid of bad examples people have been
    robert> cargo culting from.

Yeah, 

BB:approve

        Vincent