[tests] Adjust a few tests to try network requests multiple times.

tests/linker/ios/link sdk/CryptoTest.cs

@@ -81,8 +81,6 @@ public void SSL_IP_5706 ()
 			Assert.Ignore ("WatchOS doesn't support BSD sockets, which our network stack currently requires.");
 #endif
 			WebClient wc = new WebClient ();
-			// the certificate contains (several rules) the host name
-			Assert.NotNull (wc.DownloadString (NetworkResources.MicrosoftUrl));
 
 			// IP are (generally) not allowed
 			foreach (var ip in Dns.GetHostAddresses ("www.google.com")) {

tests/linker/ios/link sdk/LinkSdkRegressionTest.cs

@@ -671,10 +671,21 @@ public void WebClient_SSL_Leak ()
 #if __WATCHOS__
 			Assert.Ignore ("WatchOS doesn't support BSD sockets, which our network stack currently requires.");
 #endif
+			var exceptions = new List<string> ();
 			WebClient wc = new WebClient ();
-			// note: needs to be executed under Instrument to verify it does not leak
-			string s = wc.DownloadString (NetworkResources.MicrosoftUrl);
-			Assert.NotNull (s);
+			foreach (var url in NetworkResources.HttpsUrls) {
+				try {
+					// note: needs to be executed under Instrument to verify it does not leak
+					string s = wc.DownloadString (url);
+					Assert.NotNull (s);
+					return; // one url succeeded, that's enough
+				} catch (Exception e) {
+					var msg = $"Url '{url}' failed: {e.ToString ()}";
+					Console.WriteLine (msg); // If this keeps occurring locally for the same url, we might have to take it off the list of urls to test.
+					exceptions.Add (msg);
+				}
+			}
+			Assert.That (exceptions, Is.Empty, "At least one url should work");
 		}
 
 #if !__TVOS__ && !__WATCHOS__ && !__MACOS__

tests/linker/mac/LinkAnyTest.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using System.Net;
 using System.Net.Http;
 using System.Security.Cryptography;
@@ -63,22 +64,35 @@ public void GetWebPageAsyncTest ()
 			}
 		}
 
-		[Test]
-		public void WebClientTest ()
+		void WebClientTest (string[] urls)
 		{
-			var wc = new WebClient ();
-			var data = wc.DownloadString (NetworkResources.MicrosoftUrl);
+			var exceptions = new List<string> ();
+			foreach (var url in urls) {
+				try {
+					var wc = new WebClient ();
+					var data = wc.DownloadString (url);
+
+					Assert.That (data, Is.Not.Empty, "Downloaded content");
+					return; // one url succeeded, that's enough
+				} catch (Exception e) {
+					var msg = $"Url '{url}' failed: {e.ToString ()}";
+					Console.WriteLine (msg); // If this keeps occurring locally for the same url, we might have to take it off the list of urls to test.
+					exceptions.Add (msg);
+				}
+			}
+			Assert.That (exceptions, Is.Empty, "At least one url should work");
+		}
 
-			Assert.That (data, Is.Not.Empty, "Downloaded content");
+		[Test]
+		public void WebClientTest_Http ()
+		{
+			WebClientTest (NetworkResources.HttpUrls);
 		}
 
 		[Test]
 		public void WebClientTest_Https ()
 		{
-			var wc = new WebClient ();
-			var data = wc.DownloadString (NetworkResources.MicrosoftUrl);
-
-			Assert.That (data, Is.Not.Empty, "Downloaded content");
+			WebClientTest (NetworkResources.HttpsUrls);
 		}
 
 		[Test]
@@ -91,15 +105,26 @@ public void WebClientTest_Async ()
 
 				string data = null;
 
-				async Task GetWebPage (string url)
-				{
-					var wc = new WebClient ();
-					var task = wc.DownloadStringTaskAsync (new Uri (url));
-					data = await task;
+				var exceptions = new List<string> ();
+				foreach (var url in NetworkResources.HttpsUrls) {
+					try {
+						async Task GetWebPage (string url)
+						{
+							var wc = new WebClient ();
+							var task = wc.DownloadStringTaskAsync (new Uri (url));
+							data = await task;
+						}
+
+						GetWebPage (url).Wait ();
+						Assert.That (data, Is.Not.Empty, "Downloaded content");
+						return; // one url succeeded, that's enough
+					} catch (Exception e) {
+						var msg = $"Url '{url}' failed: {e.ToString ()}";
+						Console.WriteLine (msg); // If this keeps occurring locally for the same url, we might have to take it off the list of urls to test.
+						exceptions.Add (msg);
+					}
 				}
-
-				GetWebPage (NetworkResources.MicrosoftUrl).Wait ();
-				Assert.That (data, Is.Not.Empty, "Downloaded content");
+				Assert.That (exceptions, Is.Empty, "At least one url should work");
 			} finally {
 				SynchronizationContext.SetSynchronizationContext (current_sc);
 

tests/monotouch-test/System.Net.Http/NetworkResources.cs

@@ -9,12 +9,20 @@ public static class NetworkResources
 	{
 		public static readonly string MicrosoftUrl = "https://www.microsoft.com";
 		public static readonly Uri MicrosoftUri = new Uri (MicrosoftUrl);
+		public static readonly string MicrosoftHttpUrl = "http://www.microsoft.com";
 		public static readonly string XamarinUrl = "https://dotnet.microsoft.com/apps/xamarin";
+		public static readonly string XamarinHttpUrl = "http://dotnet.microsoft.com/apps/xamarin";
 		public static readonly Uri XamarinUri = new Uri (XamarinUrl);
 		public static readonly string StatsUrl = "https://api.imgur.com/2/stats";
 
-		public static readonly string [] Urls = {
+		public static readonly string [] HttpsUrls = {
 			MicrosoftUrl,
+			XamarinUrl,
+		};
+
+		public static readonly string [] HttpUrls = {
+			MicrosoftHttpUrl,
+			XamarinHttpUrl,
 		};
 
 		// Robots urls, useful when we want to get a small file