Handle the protocol handshake when remote end follows the spec

A recent change in the W3C spec required all responses to be
sent back wrapped in a `value` field. This is wonderful, but
makes the handshake fail. Fix that.

java/client/src/org/openqa/selenium/remote/ProtocolHandshake.java

@@ -128,6 +128,18 @@ public Result createSession(HttpClient client, Command command)
    Object w3cError = jsonBlob.get("error");
    Object ossStatus = jsonBlob.get("status");
    Map<String, ?> capabilities = null;

    // The old geckodriver prior to 0.14 returned "value" as the thing containing the session id.
    // Later versions follow the (amended) w3c spec and return the capabilities in a field called
    // "value"
    if (value != null && value instanceof Map) {
      Map<?, ?> mappedValue = (Map<?, ?>) value;
      if (mappedValue.containsKey("value") && mappedValue.containsKey("sessionId")) {
        value = mappedValue.get("value");
        sessionId = mappedValue.get("sessionId");
      }
    }

    if (value != null && value instanceof Map) {
      capabilities = (Map<String, ?>) value;
    } else if (value != null && value instanceof Capabilities) {