[xharness] Fix extension for symbolicated crash reports. (#2406)

Most browsers know that ".log" are text files, but have no idea what do do
about ".symbolicated", so change the extension to be ".log" so that it's
easier to download symbolicated crash reports.

tests/xharness/Harness.cs

@@ -735,7 +735,7 @@ namespace xharness
 				return report;
 			}
 
-			var symbolicated = new LogFile ("Symbolicated crash report", report.Path + ".symbolicated");
+			var symbolicated = new LogFile ("Symbolicated crash report", Path.ChangeExtension (report.Path, ".symbolicated.log"));
 			var environment = new Dictionary<string, string> { { "DEVELOPER_DIR", Path.Combine (XcodeRoot, "Contents", "Developer") } };
 			var rv = await ProcessHelper.ExecuteCommandAsync (symbolicatecrash, StringUtils.Quote (report.Path), symbolicated, TimeSpan.FromMinutes (1), environment);
 			if (rv.Succeeded) {;