Compile samples and integration tests with Java 8

Update the samples and integration tests to use Java 8. There's no
specific reason to keep them on Java 6 and it helps keep Eclipse happy
if we upgrade.

spring-boot-samples/spring-boot-sample-servlet/pom.xml

@@ -18,7 +18,6 @@
 	</organization>
 	<properties>
 		<main.basedir>${basedir}/../..</main.basedir>
-		<java.version>1.7</java.version>
 		<m2eclipse.wtp.contextRoot>/</m2eclipse.wtp.contextRoot>
 	</properties>
 	<dependencies>