Fix attaching ProcDump to instances when we launch xunit

We were launching xunit by ShellExecute'ing not the procdump executable,
but rather the folder that contained the procdump executable. That
really doesn't work well, it turns out.

src/Tools/Source/RunTests/Program.cs

@@ -156,7 +156,7 @@ private static void WriteLogFile(Options options)
         /// </summary>
         private static async Task HandleTimeout(Options options, CancellationToken cancellationToken)
         {
-            var procDumpFilePath = Path.Combine(options.ProcDumpPath, "procdump.exe");
+            var procDumpFilePath = GetProcDumpInfo(options).Value.ProcDumpFilePath;
 
             async Task DumpProcess(Process targetProcess, string dumpFilePath)
             {
@@ -217,7 +217,7 @@ async Task DumpProcess(Process targetProcess, string dumpFilePath)
                 var dumpDir = options.LogFilePath != null
                     ? Path.GetDirectoryName(options.LogFilePath)
                     : Directory.GetCurrentDirectory();
-                return new ProcDumpInfo(options.ProcDumpPath, dumpDir);
+                return new ProcDumpInfo(Path.Combine(options.ProcDumpPath, "procdump.exe"), dumpDir);
             }
 
             return null;