Print key for too long property values

In case of a too long property value in
SettingsToPropertiesMapper, only the value is printed, not
the key.

It makes sense also to print the key making it easier
to find what is causing the problem.

Change-Id: I3cef0d404037d3c515fae116752c4e73c6699b62

services/core/java/com/android/server/am/SettingsToPropertiesMapper.java

@@ -238,7 +238,7 @@ public class SettingsToPropertiesMapper {
             }
             value = "";
         } else if (value.length() > SYSTEM_PROPERTY_MAX_LENGTH) {
-            log(value + " exceeds system property max length.");
+            log("key=" + key + " value=" + value + " exceeds system property max length.");
             return;
         }