React to aspnet/KoreBuild#155

This converts to using Internal.AspNetCore.Sdk instead of importing from the KoreBuild folder directly

NuGet.config

@@ -3,6 +3,7 @@
   <packageSources>
     <add key="Roslyn" value="https://dotnet.myget.org/F/roslyn/api/v3/index.json" />
     <add key="AspNetCore" value="https://dotnet.myget.org/F/aspnetcore-ci-dev/api/v3/index.json" />
+    <add key="AspNetCoreTools" value="https://dotnet.myget.org/F/aspnetcore-tools/api/v3/index.json" />
     <add key="NuGet" value="https://api.nuget.org/v3/index.json" />
   </packageSources>
-</configuration>
+</configuration>

build/common.props

@@ -1,6 +1,5 @@
 <Project>
   <Import Project="..\version.props" />
-  <Import Project="..\.build\common.props" Condition="Exists('..\.build\common.props')" />
 
   <PropertyGroup>
     <Product>Microsoft ASP.NET Core</Product>
@@ -11,11 +10,8 @@
     <PublicSign Condition="'$(OS)' != 'Windows_NT'">true</PublicSign>
   </PropertyGroup>
 
-  <Target Name="EnsureInitialized"
-          BeforeTargets="Build"
-          Condition="!Exists('$(MSBuildThisFileDirectory)..\.build\common.props')">
-    <Error File="$(MSBuildProjectFile)"
-           Text="Project has not been initialized. Run 'build initialize' in the solution directory." />
-  </Target>
-  
+  <ItemGroup>
+    <PackageReference Include="Internal.AspNetCore.Sdk" Version="1.0.0-*" PrivateAssets="All" />
+  </ItemGroup>
+
 </Project>