Support multiple Http client/server components in single test

At the moment we can handle only one single Http client/server component when writing tests with YAKS. It should be possible to have multiple components and interact with these in a single test.

Something like:
```gherkin
Given Http client fooClient
Given Http client barClient

When active Http client is fooClient
And send GET /todo
Then receive Http 200 OK

When active Http client is barClient
And send GET /todo
Then receive Http 404 NOT FOUND
```