Add constants for tuple fields

Add constants for use with std::get.

Tested:  Run unit tests

Change-Id: Ic09c13feeda69d61c98f63d227cae8f08d1bf50e
Signed-off-by: Matt Spinler <spinler@us.ibm.com>
diff --git a/src/event.hpp b/src/event.hpp
index b5f1e90..b9f5167 100644
--- a/src/event.hpp
+++ b/src/event.hpp
@@ -46,7 +46,7 @@
             for (const auto& n : index)
             {
                 const auto& path = std::get<pathIndex>(n.first);
-                const auto& propertyMeta = std::get<metaIndex>(n.first);
+                const auto& propertyMeta = std::get<propertyIndex>(n.first);
                 const auto& storage = std::get<storageIndex>(n.second);
                 const auto& value = std::get<valueIndex>(storage.get());