Keep stdout for test execution

Work around microsoft/vstest#1503 by using the
MSBuild escape hatch variable MSBUILDENSURESTDOUTFORTASKPROCESSES and
ensuring that tests don't run in a disconnected MSBuild process by
passing /nr:false.

src/dotnet/commands/dotnet-test/Program.cs

@@ -32,6 +32,7 @@ public static TestCommand FromArgs(string[] args, string msbuildPath = null)
             {
                 "/t:VSTest",
                 "/v:quiet",
+                "/nodereuse:false", // workaround for https://github.com/Microsoft/vstest/issues/1503
                 "/nologo"
             };
 
@@ -95,7 +96,23 @@ public static int Run(string[] args)
                 return e.ExitCode;
             }
 
-            return cmd.Execute();
+            // Workaround for https://github.com/Microsoft/vstest/issues/1503
+            const string NodeWindowEnvironmentName = "MSBUILDENSURESTDOUTFORTASKPROCESSES";
+            string previousNodeWindowSetting = Environment.GetEnvironmentVariable(NodeWindowEnvironmentName);
+
+            int result = -1;
+
+            try
+            {
+                Environment.SetEnvironmentVariable(NodeWindowEnvironmentName, "1");
+                result = cmd.Execute();
+            }
+            finally
+            {
+                Environment.SetEnvironmentVariable(NodeWindowEnvironmentName, previousNodeWindowSetting);
+            }
+
+            return result;
         }
 
         private static string GetSemiColonEscapedString(string arg)