Rewrite all tests running with LibplanetNodeService (i.e., Swarm<T>)

[moreal]

The headless application's role is to represent network status or blockchain status as GraphQL types and to provide an interface to run Swarm<T> easily.

So its tests don't have a duty to test Swarm<T> work well. But they do that now and it makes tests slow and fails by not related with headless' features.