Checkstyle rules for imports and cleanup

Fixes #529

- enforced Spring Framework ordering rules
- disallowed static imports except for specific classes in test frameworks

spring-cloud-stream-test-support-internal/src/main/java/org/springframework/cloud/stream/test/junit/AbstractExternalResourceTestSupport.java

@@ -16,8 +16,6 @@
 
 package org.springframework.cloud.stream.test.junit;
 
-import static org.junit.Assert.fail;
-
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 import org.junit.Assume;
@@ -28,6 +26,8 @@ import org.junit.runners.model.Statement;
 
 import org.springframework.util.Assert;
 
+import static org.junit.Assert.fail;
+
 /**
  * Abstract base class for JUnit {@link Rule}s that detect the presence of some external
  * resource. If the resource is indeed present, it will be available during the test

spring-cloud-stream-test-support-internal/src/main/java/org/springframework/cloud/stream/test/junit/kafka/EmbeddedZookeeper.java

@@ -104,4 +104,4 @@ public class EmbeddedZookeeper {
 			// ignore exception
 		}
 	}
-}
+}