test: enforce generaldelta format with the right option The option that will become true by default is now 'usegeneraldelta' We have to adjust the change made in b75fed55f6dc to actually achieve its goal.

test: enforce non-generaldelta base repository in 'test-generaldelta' This test check the difference between various configurations we have to pin the type of some repositories to ensure the test is still correct when we change the default.