Update ImageCellListPage to use an image we control;

Update CellsGalleryImageUrlCellList test to wait longer than 1s for images
to load if necessary

Xamarin.Forms.Controls/GalleryPages/CellsGalleries/ImageCellListPage.cs

@@ -94,7 +94,7 @@ namespace Xamarin.Forms.Controls
 
 			var albums = new List<string> ();
 			for (int i = 0; i < 30; i++) {
-				albums.Add (string.Format ("http://cdn.instructables.com/FCP/9TOJ/GCJ0ZQV5/FCP9TOJGCJ0ZQV5.MEDIUM.jpg?ticks={0}",i ));
+				albums.Add (string.Format ("https://raw.githubusercontent.com/xamarin/Xamarin.Forms/master/Xamarin.Forms.Controls/coffee.png?ticks={0}", i ));
 			}
 
 

Xamarin.Forms.Core.iOS.UITests/Tests/Legacy-CellsUITests.cs

@@ -113,8 +113,16 @@ namespace Xamarin.Forms.Core.UITests
 
 			App.Screenshot("All ImageCells are present");
 
-			await Task.Delay(1000);
-			var numberOfImages = App.Query(q => q.Raw(PlatformViews.Image)).Length;
+			int numberOfImages = 0;
+
+			// Most of the time, 1 second is long enough to wait for the images to load, but depending on network conditions
+			// it may take longer
+			for (int n = 0; n < 30; n++)
+			{
+				await Task.Delay(1000);
+				numberOfImages = App.Query(q => q.Raw(PlatformViews.Image)).Length;
+			}
+
 			// Check that there are images present. In Android, 
 			// have to make sure that there are more than 2 for navigation.
 			Assert.IsTrue(numberOfImages > 2);