Change key value if prefix changes

Some weird looking test failures led me to track this down.
If the user changes the prefix for metric names, he probably wanted
to change the keys as welll (otherwise 2 repositories can use the
same key, which is why the test was failing for me). We can do that
in an afterPropertiesSet().

spring-boot-actuator/src/test/java/org/springframework/boot/actuate/metrics/repository/redis/RedisMetricRepositoryTests.java

@@ -44,6 +44,7 @@ public class RedisMetricRepositoryTests {
 		this.repository = new RedisMetricRepository(this.redis.getResource());
 		this.prefix = "spring.test." + System.currentTimeMillis();
 		this.repository.setPrefix(this.prefix);
+		this.repository.afterPropertiesSet();
 	}
 
 	@After