Avoiding duplicate entries on properties map

Fix #859

Instead of sending out all matching relaxed properties
we now pick up one single canonical format and send
the data to consumers using it.

Formatting settings

spring-cloud-stream-core-docs/src/main/asciidoc/spring-cloud-stream-overview.adoc

@@ -1828,8 +1828,6 @@ This module allow operators to collect metrics from stream applications without
 
 HTTP polling can be challenging on cloud environments since applications could be on a private network or behind a Load balancer that prevents per instance access.
 
-This module is included on the each of the out of box https://github.com/spring-cloud-stream-app-starters[application starters], if you want to emit metrics from your application, just import it on your pom.xml and follow the activation instructions.
-
 The module is activated when you set the destination name for its channel, `spring.cloud.stream.bindings.streamMetrics.destination=<DESTINATION_NAME>`.
 
 By default the module is configured to only send Spring Integration message channel metrics.
@@ -1866,6 +1864,35 @@ spring.cloud.stream.bindings.streamMetrics.contentType::
 +
 Default: `application/json`
 
+[NOTE]
+====
+Due to Spring Boot's https://docs.spring.io/spring-boot/docs/current/reference/html/boot-features-external-config.html#boot-features-external-config-relaxed-binding[relaxed binding] the value of a property being included can be slightly different than the original value.
+
+As a rule of thumb, the metric exporter will attempt to normalize all the properties in a consistent format using the dot notation (e.g. `JAVA_HOME` becomes `java.home`).
+
+The goal of normalization is to make downstream consumers of those metrics capable of receiving property names consistently, regardless of how they are set on the monitored application (`--spring.application.name` or `SPRING_APPLICATION_NAME` would always yield `spring.application.name`).
+
+====
+
+Below is a sample of data that is pushed to the channel in `application/json` format.
+
+[source,javascript]
+----
+{
+  "name" : "application",
+  "instanceIndex" : 0,
+  "createdTime" : "2017-03-14T13:55:38.547Z",
+  "properties" : {
+    "java.specification.version" : "1.8"
+  }
+  "metrics" : [ {
+    "name" : "mem",
+    "value" : 170757.0,
+    "timestamp" : "2017-03-14T09:55:38.547Z"
+  } ]
+}
+----
+
 == Samples
 
 For Spring Cloud Stream samples, please refer to the https://github.com/spring-cloud/spring-cloud-stream-samples[spring-cloud-stream-samples] repository on GitHub.