.NET Core App fails to load project (.NET 4.6.1 works as expected)

I created a sample .NET Console app with the following code.

```
using System;
using Microsoft.Build.Evaluation;

namespace ConsoleApp25
{
internal class Program
{
private static void Main(string[] args)
{
var buildEngine = new ProjectCollection();
var project = buildEngine.LoadProject("\\UnitTestProject.csproj");
}
}
}
```
My project references the following 2 Nuget packages:
* Microsoft.Build
* Microsoft.Build.Utilities.Core

This gives the following exception when compiled to target .NET Core 2.0;
```
Microsoft.Build.Exceptions.InvalidProjectFileException
HResult=0x80131500
Message=The SDK 'Microsoft.NET.Sdk' specified could not be found. d:\dd\GitHubTestAdapter\UnitTestProject\UnitTestProject.csproj
Source=Microsoft.Build
StackTrace:
at Microsoft.Build.Shared.ProjectErrorUtilities.ThrowInvalidProject(String errorSubCategoryResourceName, IElementLocation elementLocation, String resourceName, Object[] args) in /_/src/Shared/ProjectErrorUtilities.cs:line 412
at Microsoft.Build.Evaluation.Evaluator`4.ExpandAndLoadImportsFromUnescapedImportExpressionConditioned(String directoryOfImportingFile, ProjectImportElement importElement, List`1& projects, Boolean throwOnFileNotExistsError) in /_/src/Build/Evaluation/Evaluator.cs:line 2173
at Microsoft.Build.Evaluation.Evaluator`4.ExpandAndLoadImports(String directoryOfImportingFile, ProjectImportElement importElement) in /_/src/Build/Evaluation/Evaluator.cs:line 1944
at Microsoft.Build.Evaluation.Evaluator`4.EvaluateImportElement(String directoryOfImportingFile, ProjectImportElement importElement) in /_/src/Build/Evaluation/Evaluator.cs:line 1823
at Microsoft.Build.Evaluation.Evaluator`4.PerformDepthFirstPass(ProjectRootElement currentProjectOrImport) in /_/src/Build/Evaluation/Evaluator.cs:line 940
at Microsoft.Build.Evaluation.Evaluator`4.Evaluate(ILoggingService loggingService, BuildEventContext buildEventContext) in /_/src/Build/Evaluation/Evaluator.cs:line 726
at Microsoft.Build.Evaluation.Project.Reevaluate(ILoggingService loggingServiceForEvaluation, ProjectLoadSettings loadSettings) in /_/src/Build/Definition/Project.cs:line 2752
at Microsoft.Build.Evaluation.Project.ReevaluateIfNecessary(ILoggingService loggingServiceForEvaluation, ProjectLoadSettings loadSettings) in /_/src/Build/Definition/Project.cs:line 2719
at Microsoft.Build.Evaluation.Project.Initialize(IDictionary`2 globalProperties, String toolsVersion, String subToolsetVersion, ProjectLoadSettings loadSettings, EvaluationContext evaluationContext) in /_/src/Build/Definition/Project.cs:line 2822
at Microsoft.Build.Evaluation.Project..ctor(String projectFile, IDictionary`2 globalProperties, String toolsVersion, String subToolsetVersion, ProjectCollection projectCollection, ProjectLoadSettings loadSettings, EvaluationContext evaluationContext) in /_/src/Build/Definition/Project.cs:line 543
at Microsoft.Build.Evaluation.ProjectCollection.LoadProject(String fileName, IDictionary`2 globalProperties, String toolsVersion) in /_/src/Build/Definition/ProjectCollection.cs:line 1118
at ConsoleApp25.Program.Main(String[] args) in D:\tmp\source\repos\ConsoleApp25\ConsoleApp25\Program.cs:line 11
```

However it works as expected when targeting .NET 4.6.1

Any ideas?

[ConsoleApp25.zip](https://github.com/Microsoft/msbuild/files/2120893/ConsoleApp25.zip)