switch to devmode for integration tests

[marc0olo]

we should switch to devmode for running integration tests, example setup:

• https://github.com/marc0olo/ae-devmode-test

[marc0olo]

I wanna have a bundle of the node with mdw and devmode. so far it's not available. we need to wait for that

[marc0olo]

seems like we cannot expect a bundle that includes mdw in the near future. will probably continue using our self built node-mdw bundle.

background info: aeternity/ae_mdw#334

[marc0olo]

alternatively we can isolate tests that require the mdw and use devmode for other tests.