Fix test E2E test fixture to honor the workerRuntime environment variables

[_functionsWorkerLanguage](https://github.com/Azure/azure-functions-host/blob/dev/test/WebJobs.Script.Tests.Integration/ScriptHostEndToEnd/ScriptHostEndToEndTestFixture.cs#L39) set by [ScriptHostEndToEndTestFixture.cs](https://github.com/Azure/azure-functions-host/blob/dev/test/WebJobs.Script.Tests.Integration/ScriptHostEndToEnd/ScriptHostEndToEndTestFixture.cs#L39) is not honored.

PR #3824 moved initializing rpc server and java language worker as of [common services](https://github.com/Azure/azure-functions-host/blob/dev/src/WebJobs.Script/ScriptHostBuilderExtensions.cs#L164)

Initializing rpc server and language worker happen before the builder in the test fixture is invoked.

This causes java worker to start even though not needed.