[#106] Converted UUID to Long

- Changed Random instantiation to a shared Random
- Changed the name of the converter
- Changed generator into random
- Span id is now non-nullable.
    - it gets generated in the http filter if it's not there
    - it's generated in the spring-integration channels if it wasn't set

spring-cloud-sleuth-samples/spring-cloud-sleuth-sample-zipkin/src/test/java/integration/ZipkinTests.java

@@ -31,10 +31,11 @@ import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.test.context.TestPropertySource;
 import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
-import org.springframework.util.JdkIdGenerator;
 import sample.SampleZipkinApplication;
 import tools.AbstractIntegrationTest;
 
+import java.util.Random;
+
 @RunWith(SpringJUnit4ClassRunner.class)
 @SpringApplicationConfiguration(classes = { WaitUntilZipkinIsUpConfig.class,
 		SampleZipkinApplication.class })
@@ -53,9 +54,8 @@ public class ZipkinTests extends AbstractIntegrationTest {
 	}
 
 	@Test
-	@SneakyThrows
 	public void should_propagate_spans_to_zipkin() {
-		String traceId = new JdkIdGenerator().generateId().toString();
+		long traceId = new Random().nextLong();
 
 		await().until(httpMessageWithTraceIdInHeadersIsSuccessfullySent(
 				sampleAppUrl + "/hi2", traceId));