Use Log4J message template instead of String.format (#1673)

* Factorise metrics code for KeyValueStorage database

- introduce `MonitorableKeyValueStorage`
- factorise code
- remove metrics instanciation in `RocksDbKeyValueStorage` and `ColumnarRocksDbKeyValueStorage`

* Rename class

* Use Log4J message template instead of String.format

ethereum/jsonrpc/src/main/java/tech/pegasys/pantheon/ethereum/jsonrpc/internal/methods/AdminChangeLogLevel.java

@@ -44,7 +44,7 @@ public String getName() {
   public JsonRpcResponse response(final JsonRpcRequest request) {
     try {
       final Level logLevel = parameters.required(request.getParams(), 0, Level.class);
-      LOG.log(Level.OFF, String.format("Setting logging level to %s", logLevel.name()));
+      LOG.log(Level.OFF, "Setting logging level to {}", logLevel.name());
       Configurator.setAllLevels("", logLevel);
       return new JsonRpcSuccessResponse(request.getId());
     } catch (InvalidJsonRpcParameters invalidJsonRpcParameters) {