PluggableDiscovery: add special case for property "." (self)

"Self" property scans for board identifier instead than on property keys.
This stuff must be introduced to allow backwards compatibility with existing OTA mdns TXT properties.

Author: facchinm

arduino-core/src/cc/arduino/packages/BoardPort.java

@@ -176,6 +176,10 @@ public boolean matchesBoard(TargetBoard board) {
         if (suffix >= 0) {
           prop += "." + suffix;
         }
+        if (prop == ".") {
+          found = (board.getId().equals(value));
+          break;
+        }
         if (!boardProps.containsKey(prop)) {
           return false;
         }