asio: Added utility functions getProperty and setProperty

Tested:
  - Modified one of the examples to use this utility instead
  - All other tests are still passing after this change

Change-Id: I3237e281915c7edf931e3326b88bd24714ee8ecb
Signed-off-by: Krzysztof Grobelny <krzysztof.grobelny@intel.com>
diff --git a/example/get-all-properties.cpp b/example/get-all-properties.cpp
index 8e7ee54..7a2d037 100644
--- a/example/get-all-properties.cpp
+++ b/example/get-all-properties.cpp
@@ -1,7 +1,7 @@
 #include <boost/asio.hpp>
 #include <sdbusplus/asio/connection.hpp>
-#include <sdbusplus/asio/get_all_properties.hpp>
 #include <sdbusplus/asio/object_server.hpp>
+#include <sdbusplus/asio/property.hpp>
 #include <sdbusplus/bus.hpp>
 #include <sdbusplus/unpack_properties.hpp>