Use dotnet/scenario-tests for testing .NET container images

[lbussell]

There exists some new infrastructure for shared .NET scenario tests in https://github.com/dotnet/scenario-tests. These tests should be able to run against any installation of .NET.

Instead of defining separate scenario tests in this repo (Microsoft.DotNet.Docker.Tests/TestScenarios), we should try to apply the shared scenario tests to this repo. If they don't work well for the Docker image use case, we should consider providing feedback or contributing features that allow them to function for our scenario.