test_changeChildReactor fails without installed ampoule

[Marien Zwart]

test_changeChildReactor does not pass packages=("twisted", "ampoule") to its ProcessStarter, which means the test fails if there is no system-wide ampoule for the child to pick up. This seems like a simple oversight: all other ProcessStarter calls do pass it, and doing the same thing here makes the test pass on my system.