Wrap command should not create wrap folder if project with same name already exists

[davidfowl]

In this scenario, the library author has the following layout:

src/Autofac/project.json
src/Autofac/Autofac.PCL.csproj
src/Autofac/Autofac.Net40.csproj

Calling kpm wrap Autofac.PCL.csproj and kpm wrap Autofac.Net40.csproj should update the project.json, but today is creating wrap/Autofac/project.json. It should only add update global.json if any project was written to the wrap folder. As part of this work, properties that we add to the existing project.json files should not overwrite what is already there.