Bump test projects up to .NET 4.5.2

- aspnet/Testing#248
- xUnit no longer supports .NET 4.5.1
- build tests for desktop .NET only on Windows

Author: dougbu

test/Microsoft.AspNetCore.Identity.EntityFrameworkCore.InMemory.Test/Microsoft.AspNetCore.Identity.EntityFrameworkCore.InMemory.Test.csproj

@@ -1,7 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <Import Project="..\..\build\common.props" />
   <PropertyGroup>
-    <TargetFrameworks>netcoreapp1.1;net451</TargetFrameworks>
+    <TargetFrameworks>netcoreapp1.1;net452</TargetFrameworks>
+    <TargetFrameworks Condition=" '$(OS)' != 'Windows_NT' ">netcoreapp1.1</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="..\Shared\*.cs" />

test/Microsoft.AspNetCore.Identity.EntityFrameworkCore.Test/Microsoft.AspNetCore.Identity.EntityFrameworkCore.Test.csproj

@@ -1,7 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <Import Project="..\..\build\common.props" />
   <PropertyGroup>
-    <TargetFrameworks>netcoreapp1.1;net451</TargetFrameworks>
+    <TargetFrameworks>netcoreapp1.1;net452</TargetFrameworks>
+    <TargetFrameworks Condition=" '$(OS)' != 'Windows_NT' ">netcoreapp1.1</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="..\Shared\*.cs" />

test/Microsoft.AspNetCore.Identity.InMemory.Test/Microsoft.AspNetCore.Identity.InMemory.Test.csproj

@@ -1,7 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <Import Project="..\..\build\common.props" />
   <PropertyGroup>
-    <TargetFrameworks>netcoreapp1.1;net451</TargetFrameworks>
+    <TargetFrameworks>netcoreapp1.1;net452</TargetFrameworks>
+    <TargetFrameworks Condition=" '$(OS)' != 'Windows_NT' ">netcoreapp1.1</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="..\Shared\*.cs" />

test/Microsoft.AspNetCore.Identity.Test/Microsoft.AspNetCore.Identity.Test.csproj

@@ -1,7 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <Import Project="..\..\build\common.props" />
   <PropertyGroup>
-    <TargetFrameworks>netcoreapp1.1;net451</TargetFrameworks>
+    <TargetFrameworks>netcoreapp1.1;net452</TargetFrameworks>
+    <TargetFrameworks Condition=" '$(OS)' != 'Windows_NT' ">netcoreapp1.1</TargetFrameworks>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="..\Shared\*.cs" />