VS2017 using dotnet command

1. Add a reference to Microsoft.EntityFrameworkCore.Tools
2. After adding the reference, it prompts that the command "dotnet ef" was not found and adds the following node to the csprog file

   <ItemGroup>
       <DotNetCliToolReference Include="Microsoft.EntityFrameworkCore.Tools.DotNet" Version="2.0.0" />
   </ItemGroup>