[One .NET] Fix <InstallAndroidDependencies/> target and test

Context: xamarin/android-sdk-installer#450

A fix for the `<InstallAndroidDependencies/>` target has been brought in
via the `android-sdk-installer` bump.

The `<ResolveAndroidTooling/>` task has been updated to ensure that the
`AndroidApilevel` output will be set regardless of whether or not the
task fails when detecting Android SDK components.  This allows Android
SDK provisioning to succeed for One .NET builds when the Android SDK is
missing entirely or just missing some components.  Previous behavior
attempted to determine which `android.jar` to install based on the
`$(TargetFrameworkVersion)` of the project, which is not a valid
comparison in One .NET projects.

The `<InstallAndroidDependencies/>` test previously had issues due to
clean up logic in the test framework that partially deleted the newly
provisioned Android SDK on a subsequent build.  I believe that we've
been seeing successful results for this test because the subsequent
build in the test would fall back to a different Android SDK that was
already on disk.  The test has been improved by asserting that the newly
installed Android SDK is used during the subsequent build.

Author: pjcollins

.external

@@ -1,2 +1,2 @@
-xamarin/monodroid:master@5784a746112babd9ef801e0a6bc3fe2694bdf64c
+xamarin/monodroid:dev/pjc/fix-win-installtask@dd1eeab333de9b590d8bb166d230df7d5bf2be96
 mono/mono:2020-02@83105ba22461455f4343d6bb14976eba8b0b3f39

src/Xamarin.Android.Build.Tasks/Tasks/ResolveAndroidTooling.cs

@@ -79,6 +79,7 @@ public class ResolveAndroidTooling : AndroidTask
 
 		public override bool RunTask ()
 		{
+			AndroidApiLevel = GetMaxStableApiLevel ().ToString ();
 			string toolsZipAlignPath = Path.Combine (AndroidSdkPath, "tools", ZipAlign);
 			bool findZipAlign = (string.IsNullOrEmpty (ZipAlignPath) || !Directory.Exists (ZipAlignPath)) && !File.Exists (toolsZipAlignPath);
 
@@ -192,8 +193,7 @@ public override bool RunTask ()
 
 		protected virtual bool Validate ()
 		{
-			AndroidApiLevel = GetMaxStableApiLevel ().ToString ();
-			return true;
+			return !string.IsNullOrEmpty (AndroidApiLevel);
 		}
 
 		protected virtual void LogOutputs ()

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/AndroidDependenciesTests.cs

@@ -6,7 +6,7 @@
 namespace Xamarin.Android.Build.Tests
 {
 	[TestFixture]
-	[Category ("Node-3")]
+	[Category ("Node-3"), Category ("dotnet")]
 	[NonParallelizable] // Do not run environment modifying tests in parallel.
 	public class AndroidDependenciesTests : BaseTest
 	{
@@ -19,13 +19,19 @@ public void InstallAndroidDependenciesTest ()
 			try {
 				string sdkPath = Path.Combine (Root, "temp", TestName, "android-sdk");
 				Environment.SetEnvironmentVariable ("ANDROID_SDK_PATH", sdkPath);
+				if (Directory.Exists (sdkPath))
+					Directory.Delete (sdkPath, true);
+				Directory.CreateDirectory (sdkPath);
 				var proj = new XamarinAndroidApplicationProject ();
 				using (var b = CreateApkBuilder ()) {
+					b.CleanupAfterSuccessfulBuild = false;
 					string defaultTarget = b.Target;
 					b.Target = "InstallAndroidDependencies";
 					Assert.IsTrue (b.Build (proj, parameters: new string [] { "AcceptAndroidSDKLicenses=true" }), "InstallAndroidDependencies should have succeeded.");
 					b.Target = defaultTarget;
-					Assert.IsTrue (b.Build (proj), "build should have succeeded.");
+					Assert.IsTrue (b.Build (proj, true), "build should have succeeded.");
+					Assert.IsTrue (b.LastBuildOutput.ContainsText ($"Output Property: _AndroidSdkDirectory={sdkPath}"), "_AndroidSdkDirectory was not set to new SDK path.");
+					Assert.IsTrue (b.LastBuildOutput.ContainsText ($"JavaPlatformJarPath={sdkPath}"), "JavaPlatformJarPath did not contain new SDK path.");
 				}
 			} finally {
 				Environment.SetEnvironmentVariable ("ANDROID_SDK_PATH", old);