Assembly scanner improvements

- Allow to configure the Assembly scanner to not throw exceptions
- If we find a valid `IEndpointConfig`, we should skip scanning
- If there are errors, but if we can find endpoint config, we continue, but don't pass in bad assemblies.
So only do this if there are no errors:
```c#
 if (arguments.ScannedAssemblies.Count > 0 -- && no errors)
 {
 serviceCommandLine.AddRange(arguments.ScannedAssemblies.Select(assembly =>    String.Format(@"/scannedAssemblies:""{0}""", assembly)));
 }
```
- The host should not throw, so that we can still start the endpoint `AppDomain` so that any binding redirects kick in