Porting corefx PRs 7936 and 7989
Porting corefx PRs 7936 and 7989

* PR #7936 - Stop the build if package restore failed. (Only touched build.proj)
* PR #7989 - Validate that the results of a restore are exactly what was requested
   Required build tools update.
   Immediately caught version errors with System.Net.Http, System.Private.ServiceModel and System.Runtime.Extensions which are also fixed in this PR.

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