[xharness] Add support for specifying whether variations should be generated for Xamarin.iOS projects.

tests/xharness/Harness.cs

@@ -491,7 +491,7 @@ namespace Xharness {
 			foreach (var monoNativeInfo in IOSTestProjects.Where (x => x.MonoNativeInfo != null).Select (x => x.MonoNativeInfo))
 				monoNativeInfo.Convert ();
 
-			foreach (var proj in IOSTestProjects) {
+			foreach (var proj in IOSTestProjects.Where ((v) => v.GenerateVariations).ToArray ()) {
 				var file = proj.Path;
 
 				if (!File.Exists (file)) {

tests/xharness/Microsoft.DotNet.XHarness.iOS.Shared/MacTestProject.cs

@@ -16,11 +16,14 @@ namespace Microsoft.DotNet.XHarness.iOS.Shared {
 		public bool GenerateFull => GenerateVariations && (TargetFrameworkFlavors & MacFlavors.Full) == MacFlavors.Full;
 		public bool GenerateSystem => GenerateVariations && (TargetFrameworkFlavors & MacFlavors.System) == MacFlavors.System;
 
-		public bool GenerateVariations {
+		public override bool GenerateVariations {
 			get {
 				// If a bitwise combination of flavors, then we're generating variations
 				return TargetFrameworkFlavors != MacFlavors.Modern && TargetFrameworkFlavors != MacFlavors.Full && TargetFrameworkFlavors != MacFlavors.System && TargetFrameworkFlavors != MacFlavors.Console;
 			}
+			set {
+				throw new Exception ("This value is read-only");
+			}
 		}
 
 		public string Platform = "x86";

tests/xharness/Microsoft.DotNet.XHarness.iOS.Shared/TestProject.cs

@@ -13,6 +13,7 @@ namespace Microsoft.DotNet.XHarness.iOS.Shared {
 	public class TestProject
 	{
 		XmlDocument xml;
+		bool generate_variations = true;
 
 		public string Path;
 		public string SolutionPath;
@@ -42,6 +43,8 @@ namespace Microsoft.DotNet.XHarness.iOS.Shared {
 			IsExecutableProject = isExecutableProject;
 		}
 
+		public virtual bool GenerateVariations { get => generate_variations; set => generate_variations = value; }
+
 		public XmlDocument Xml {
 			get {
 				if (xml == null) {