Rename exercises dir

Name it instead "topics" so it won't be
strange if some topics included "exercises" directory.

topics/aws/exercises/no_application/exercise.md

@@ -0,0 +1,8 @@
+## No Application :'(
+
+### Objectives
+
+Explain what might be possible reasons for the following issues:
+
+1. Getting "time out" when trying to reach an application running on EC2 instance
+2. Getting "connection refused" error