Convert all sample tests to @IntegrationTest where appropriate

Makes them a lot more readable IMO, and also enables @Autowiring
from the context into the test case (sweeet). I added @DirtiesContext
to all of them as well to be on the safe side, but possbly that can be
optimized in some way as well.

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

@@ -16,7 +16,6 @@
 		<dependency>
 			<groupId>org.springframework.boot</groupId>
 			<artifactId>spring-boot-starter-security</artifactId>
-			<version>${project.version}</version>
 		</dependency>
 		<dependency>
 			<groupId>org.springframework.boot</groupId>