Clearing cache corrupts paket tool

Description

Running dotnet paket clear-cache command causes paket to become corrupt and unusable

Repro steps

1. Install paket locally in an application using dotnet core dotnet new tool-manifest, dotnet tool install paket, dotnet tool restore
2. Run dotnet paket clear-cache:

C:\repos\MyApp> dotnet paket clear-cache
Paket version 5.247.4
  - C:\Users\vitor\.nuget\packages
Performance:
 - Runtime: 1 second
Paket failed with
-> UnauthorizedAccessException: Access to the path 'C:\Users\vitor\.nuget\packages\paket\5.247.4\tools\netcoreapp2.1\any\Argu.dll' is denied.

1. Paket carshes and becomes corrupt:

C:\repos\MyApp>dotnet paket --version
A fatal error was encountered. The library 'hostpolicy.dll' required to execute the application was not found in 'C:\Users\vitor\.nuget\packages\paket\5.247.4\tools\netcoreapp2.1\any\'.
Failed to run as a self-contained app. If this should be a framework-dependent app, add the C:\Users\vitor\.nuget\packages\paket\5.247.4\tools\netcoreapp2.1\any\paket.runtimeconfig.json file specifying the appropriate framework.

[ChrSteinert]

I’d say the clear-cache should

• be more robust against undeletable files, and
• show a warning, that paket local tools might be deleted.

Opinions, @forki ?

[ChrSteinert]

The current cache-clear just tries to delete every file in the common nuget cache folders recursively. I can use some better erorr handling though 😉 (And a warning cannot hurt as well)