netty: Use DefaultELG with LocalChannel in test

LocalChannel is not guaranteed to be compatible with NioEventLoopGroup,
and is failing with Netty 4.2.0.Alpha3-SNAPSHOT.

See #11447

netty/src/test/java/io/grpc/netty/NettyClientTransportTest.java

@@ -82,6 +82,7 @@
 import io.netty.channel.ChannelHandlerContext;
 import io.netty.channel.ChannelOption;
 import io.netty.channel.ChannelPromise;
+import io.netty.channel.DefaultEventLoopGroup;
 import io.netty.channel.EventLoopGroup;
 import io.netty.channel.ReflectiveChannelFactory;
 import io.netty.channel.local.LocalChannel;
@@ -519,15 +520,20 @@ public void channelFactoryShouldSetSocketOptionKeepAlive() throws Exception {
   @Test
   public void channelFactoryShouldNNotSetSocketOptionKeepAlive() throws Exception {
     startServer();
-    NettyClientTransport transport = newTransport(newNegotiator(),
-        DEFAULT_MAX_MESSAGE_SIZE, GrpcUtil.DEFAULT_MAX_HEADER_LIST_SIZE, "testUserAgent", true,
-        TimeUnit.SECONDS.toNanos(10L), TimeUnit.SECONDS.toNanos(1L),
-        new ReflectiveChannelFactory<>(LocalChannel.class), group);
+    DefaultEventLoopGroup group = new DefaultEventLoopGroup(1);
+    try {
+      NettyClientTransport transport = newTransport(newNegotiator(),
+          DEFAULT_MAX_MESSAGE_SIZE, GrpcUtil.DEFAULT_MAX_HEADER_LIST_SIZE, "testUserAgent", true,
+          TimeUnit.SECONDS.toNanos(10L), TimeUnit.SECONDS.toNanos(1L),
+          new ReflectiveChannelFactory<>(LocalChannel.class), group);
 
-    callMeMaybe(transport.start(clientTransportListener));
+      callMeMaybe(transport.start(clientTransportListener));
 
-    assertThat(transport.channel().config().getOption(ChannelOption.SO_KEEPALIVE))
-        .isNull();
+      assertThat(transport.channel().config().getOption(ChannelOption.SO_KEEPALIVE))
+          .isNull();
+    } finally {
+      group.shutdownGracefully(0, 10, TimeUnit.SECONDS);
+    }
   }
 
   @Test