[kohttp][test] Split tests into unit and integration groups

[rybalkinsd]

1. Introduce a way to group tests into unit and integration
2. Run unit first during build stage, and integration only after successful run of units.
3. Many of existing integration tests could be replaced with unit + mocks, it will improve test time

[rybalkinsd]

cc @GolovPavel

[GolovPavel]

Hi! I found, that we have tests in both gradle modules: kohttp and kohttp-test. By what principle are tests divided into modules?

[rybalkinsd]

Hi! I found, that we have tests in both gradle modules: kohttp and kohttp-test. By what principle are tests divided into modules?

https://github.com/rybalkinsd/kohttp/pull/193#issuecomment-632172277