Fix projectmodel-server regression

1. Address the null reference exception when a project dependency is
broken.
2. Address the duplicate key issues after the logic of redirecting
System pacage to reference assembly was added

Update projectmodel-server and tests

1. Fix test timeout caused by undisconnected socket;
2. Update project model server

test/dotnet-projectmodel-server.Tests/DthTestClient.cs

@@ -9,6 +9,7 @@ using System.Net;
 using System.Net.Sockets;
 using System.Threading;
 using System.Threading.Tasks;
+using Microsoft.Extensions.Logging;
 using Newtonsoft.Json;
 using Xunit;
 
@@ -29,18 +30,19 @@ namespace Microsoft.DotNet.ProjectModel.Server.Tests
         // works in visual studio
         private readonly Dictionary<string, int> _projectContexts = new Dictionary<string, int>();
         private int _nextContextId;
+        private readonly Socket _socket;
 
         public DthTestClient(DthTestServer server)
         {
-            var socket = new Socket(AddressFamily.InterNetwork,
-                                    SocketType.Stream,
-                                    ProtocolType.Tcp);
+            _socket = new Socket(AddressFamily.InterNetwork,
+                                 SocketType.Stream,
+                                 ProtocolType.Tcp);
 
-            socket.Connect(new IPEndPoint(IPAddress.Loopback, server.Port));
+            _socket.Connect(new IPEndPoint(IPAddress.Loopback, server.Port));
 
             _hostId = server.HostId;
 
-            _networkStream = new NetworkStream(socket);
+            _networkStream = new NetworkStream(_socket);
             _reader = new BinaryReader(_networkStream);
             _writer = new BinaryWriter(_networkStream);
 
@@ -221,6 +223,7 @@ namespace Microsoft.DotNet.ProjectModel.Server.Tests
             _writer.Dispose();
             _networkStream.Dispose();
             _readCancellationToken.Cancel();
+            _socket.Shutdown(SocketShutdown.Both);
         }
 
         private void ReadMessage(CancellationToken cancellationToken)

test/dotnet-projectmodel-server.Tests/DthTestServer.cs

@@ -5,13 +5,14 @@ using System;
 using System.Net;
 using System.Net.Sockets;
 using System.Threading;
+using Microsoft.DotNet.ProjectModel.Server;
 using Microsoft.Extensions.Logging;
 
 namespace Microsoft.DotNet.ProjectModel.Server.Tests
 {
     public class DthTestServer : IDisposable
     {
-        private readonly Program _program;
+        private readonly ProjectModelServerCommand _program;
         private readonly Thread _thread;
 
         public DthTestServer(ILoggerFactory loggerFactory)
@@ -21,9 +22,9 @@ namespace Microsoft.DotNet.ProjectModel.Server.Tests
             Port = FindFreePort();
             HostId = Guid.NewGuid().ToString();
 
-            _program = new Program(Port, HostId, LoggerFactory);
+            _program = new ProjectModelServerCommand(Port, HostId, LoggerFactory);
 
-            _thread = new Thread(() => { _program.OpenChannel(); });
+            _thread = new Thread(() => { _program.OpenChannel(); }) { IsBackground = true };
             _thread.Start();
         }
 

test/dotnet-projectmodel-server.Tests/DthTests.cs

@@ -86,7 +86,7 @@ namespace Microsoft.DotNet.ProjectModel.Server.Tests
         [Theory]
         [InlineData("Project", "UnresolvedProjectSample", "EmptyLibrary", "Project")]
         [InlineData("Package", "UnresolvedPackageSample", "NoSuchPackage", null)]
-        [InlineData("Package", "IncompatiblePackageSample", "Newtonsoft.Json", "Package")]
+        [InlineData("Package", "IncompatiblePackageSample", "Microsoft.Web.Administration", "Package")]
         public void DthCompilation_Initialize_UnresolvedDependency(string referenceType,
                                                                    string testProjectName,
                                                                    string expectedUnresolvedDependency,