[xharness] Handle UTF8 text better. (#8065)

* Set UTF8 as the encoding for process output.
* Serve plain text as UTF-8 plain text from our test server.

This makes emojiis render as emojiis 😁😁😁

tests/xharness/Execution/ProcessManager.cs

@@ -76,6 +76,9 @@ namespace Xharness.Execution {
 
 			process.StartInfo.RedirectStandardError = true;
 			process.StartInfo.RedirectStandardOutput = true;
+			// Make cute emojiis show up as cute emojiis in the output instead of ugly text symbols!
+			process.StartInfo.StandardOutputEncoding = Encoding.UTF8; 
+			process.StartInfo.StandardErrorEncoding = Encoding.UTF8;
 			process.StartInfo.UseShellExecute = false;
 
 			if (environment_variables != null) {

tests/xharness/Jenkins/Jenkins.cs

@@ -1586,7 +1586,7 @@ namespace Xharness.Jenkins
 										response.ContentType = "image/png";
 										break;
 									default:
-										response.ContentType = System.Net.Mime.MediaTypeNames.Text.Plain;
+										response.ContentType = System.Net.Mime.MediaTypeNames.Text.Plain + ";charset=UTF-8";
 										break;
 									}
 									while ((read = fs.Read (buffer, 0, buffer.Length)) > 0)
@@ -1880,7 +1880,7 @@ namespace Xharness.Jenkins
 				writer.WriteLine ("<h1>Test results</h1>");
 
 				foreach (var log in Logs)
-					writer.WriteLine ("<span id='x{2}' class='autorefreshable'> <a href='{0}' type='text/plain'>{1}</a></span><br />", log.FullPath.Substring (LogDirectory.Length + 1), log.Description, id_counter++);
+					writer.WriteLine ("<span id='x{2}' class='autorefreshable'> <a href='{0}' type='text/plain;charset=UTF-8'>{1}</a></span><br />", log.FullPath.Substring (LogDirectory.Length + 1), log.Description, id_counter++);
 
 				var headerColor = "black";
 				if (unfinishedTests.Any ()) {
@@ -2197,6 +2197,9 @@ namespace Xharness.Jenkins
 									case "text/xml":
 										log_target = "_top";
 										break;
+									case "text/plain":
+										log_type += ";charset=UTF-8";
+										goto default;
 									default:
 										log_target = "_self";
 										break;