Make AbstractBinderTests more Spring-friendly

Right now AbstractBinderTests doesn't allow to inject external ApplicationContext for internal components to test.

For example I would like to have something like:

@EnableBinding
static class Config {

	@Bean
	public PartitionTestSupport partitionSupport() {
		return new PartitionTestSupport();
	}

}

and use it from the:

public KinesisTestBinder(AmazonKinesisAsync amazonKinesis,
		KinesisBinderConfigurationProperties kinesisBinderConfigurationProperties) {

	this.applicationContext = new AnnotationConfigApplicationContext(Config.class);

Then this application context should be available in all support methods in the AbstractBinderTests for example that partitionSupport bean should be available from the createBindableChannel() to properly bind all the necessary Spring Cloud Stream infrastructure into the channel we expect.

Start by reading AbstractBinderTests and the KinesisTestBinder constructor, then trace createBindableChannel() and the existing application-context setup shown in the issue. The change is complete when an externally supplied Config context, including its partitionSupport bean, is available to the AbstractBinderTests support methods and the expected binding infrastructure is created.