Tools CLI ask

1. Need to be in user directory
   Or at least an option to say “only user directory”. Current all global tool is user level, since we don’t want to require user to run with sudo. While today’s NuGet cache could be user level or machine level.

2. All the “format”
   This is due to weird behavior when using profile.d and paths.d adding to PATH. For mac, if we want to add user directory using paths.d. It has to be in ~/.nuget/ toolsdir format (before tilde expansion). And for Linux using profile.d, it has to be $HOME/.nuget/toolsplace format. The full path will also be used to display message to user. To make such API look nice turned out is hard.