Sdk: Need command list installed runtimes and SDKs

[rkeithhill]

Steps to reproduce

Tell a project contributor to find out which versions of the .NET Core SDK they have installed to help you troubleshoot a build problem they are having.

Expected behavior

You tell the user to run dotnet list to get a list of installed runtimes and SDKs. Or perhaps there is a switch to control which is listed.

Actual behavior

Basically you tell them this for the runtimes:

Operating System | Location
-- | --
Windows | C:Program FilesdotnetsharedMicrosoft.NETCore.App
macOS | /usr/local/share/dotnet/shared/Microsoft.NETCore.App/
Supported Linux platforms | /usr/share/dotnet/shared/Microsoft.NETCore.App/

and to dir another set of directories for the SDKs. That's a spew.

Environment data

dotnet --info output:

.NET Command Line Tools (2.0.0)

Product Information:
 Version:            2.0.0
 Commit SHA-1 hash:  cdcd1928c9

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.16299
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\2.0.0\

Microsoft .NET Core Shared Framework Host

  Version  : 2.0.0
  Build    : e8b8861ac7faf042c87a5c2f9f2d04c98b69f28d

[tmds]

--list-sdks and --list-runtimes have been added here: https://github.com/dotnet/core-setup/pull/3132
These are not yet in a released version.

[rkeithhill]

Duplicate of dotnet/sdk#8751