dotnet tools shouldn't error if no arguments are provided

Just print the help and drop the "Required command was not provided." .e.g

```
root@004561cfab39:/# dotnet counters
Required command was not provided.

Usage:
dotnet-counters [options] [command]

Options:
--version Display version information

Commands:
monitor Start monitoring a .NET application
list Display a list of counter names and descriptions, grouped by provider.
list-processes Display a list of dotnet processes that can be monitored.
```