added support for onChange report

Report is now notified when metric changes and updates reading values.

Tested:
  - Added new unit tests
  - OnChange report updates Readings when metric values changes

Change-Id: I3be9ef7aa0486cb15bac627aa1de5cc632613b3b
Signed-off-by: Krzysztof Grobelny <krzysztof.grobelny@intel.com>
diff --git a/src/report_factory.cpp b/src/report_factory.cpp
index 039846e..0d7f011 100644
--- a/src/report_factory.cpp
+++ b/src/report_factory.cpp
@@ -26,7 +26,7 @@
     std::vector<LabeledMetricParameters> labeledMetricParams,
     bool enabled) const
 {
-    std::vector<std::shared_ptr<interfaces::Metric>> metrics = utils::transform(
+    auto metrics = utils::transform(
         labeledMetricParams,
         [this](const LabeledMetricParameters& param)
             -> std::shared_ptr<interfaces::Metric> {