Bump to xamarin/xamarin-android-tools/master@bfb66f38 (#561)

Changes: dotnet/android-tools@66d445c...bfb66f3

Context: https://devdiv.visualstudio.com/DevDiv/_workitems/edit/826178
Context: https://devdiv.visualstudio.com/DevDiv/_workitems/edit/938504
Context: http://feedback.devdiv.io/606218

  * dotnet/android-tools@bfb66f3: Update to sdk-style csproj and netstandard2.0. (#78)
  * dotnet/android-tools@9f4ed4b: Use %ProgramW6432% path for 32-bit apps (#75)
  * dotnet/android-tools@294f447: Merge pull request #77 from xamarin/dev/soch/fix_certs
  * dotnet/android-tools@131bb29: Fix authenticode certs
  * dotnet/android-tools@962c486: Prevent NRE when Android SDK is not found (#73)
  * dotnet/android-tools@9b03310: [Windows] check %JAVA_HOME% for locating Jdk (#74)
  * dotnet/android-tools@cb41333: Get OpenJDK from well-known paths, not just registry (#72)
  * dotnet/android-tools@53ffdae: Downgrade to net46 for compatibility with VS2017+(#69)
  * dotnet/android-tools@4264703: Add AlternateIds for 9.0
  * dotnet/android-tools@90a6e06: [Xamarin.Android.Tools.AndroidSdk] Add 9.0 to KnownVersions.
  * dotnet/android-tools@4f717b6: Check if the path exists before trying to enumerate it. (#67)

Had to add an explicit NuGet restore to build it on Windows because 🤷‍♂.

Author: jpobst

build-tools/automation/azure-pipelines.yaml

@@ -26,6 +26,15 @@ jobs:
     inputs:
       version: $(DotNetCoreVersion)
 
+  - task: NuGetToolInstaller@0
+    inputs:
+      versionSpec: 5.x
+
+  - task: NuGetCommand@2
+    inputs:
+      command: restore
+      restoreSolution: 'external\xamarin-android-tools\Xamarin.Android.Tools.sln'
+      
   - task: MSBuild@1
     displayName: MSBuild Java.Interop.sln /t:Prepare
     inputs: