Add Test Env. Variable; Remove Bogus Test File

Spring Integration components that create messages require
a `BeanFactory` to get access to the configured `MessageBuilderFactory`.

An environment variable `SI_FATAL_WHEN_NO_BEANFACTORY` helps developers
by treating a missing bean factory as fatal.

Spring XD (particularly in message bus implementations) programmatically
creates many SI components; we need to ensure such components get a bean
factory.

Set the environment variable when running test cases.

This has the (unfortunate) side effect of requiring a bean factory
for components created programmatically in test cases. In this case
simply inject `mock(BeanFactory.class)`.

Also remove an invalid test class from `spring-xd-hadoop`.