Porting Corefx PR #8318
Porting Corefx PR #8318

* Specify corefx packages to convert when generating a project.json for test.

KKhurin/wcf,MattGal/wcf,zhenlan/wcf,ericstj/wcf,KKhurin/wcf,StephenBonikowsky/wcf,imcarolwang/wcf,ElJerry/wcf,hongdai/wcf,dotnet/wcf,shmao/wcf,imcarolwang/wcf,iamjasonp/wcf,StephenBonikowsky/wcf,zhenlan/wcf,hongdai/wcf,dotnet/wcf,dotnet/wcf,imcarolwang/wcf,mconnew/wcf,MattGal/wcf,ElJerry/wcf,ericstj/wcf,iamjasonp/wcf,mconnew/wcf,mconnew/wcf,shmao/wcf