add DL test

[yito88]

https://scalar-labs.atlassian.net/browse/DLT-2312

• [x] Setup DB and DL server
• [x] Add the runner
• [x] Add a simple test
• [x] Add nemeses
• [x] Switch a server
• [x] Handle an unknown failure

I've added a simple test. I'll add transfer test at another PR.