teams/cloud/wsl: Use native "wsl" image type

This introduces extra validation for WSL image creation to ensure
the result is usable.

tmt/plans/wsl/build.fmf

@@ -2,7 +2,7 @@ summary: Build the Windows Subsystem for Linux image
 discover:
     how: fmf
 environment:
-    image_type: tbz
+    image_type: wsl
     image_profile: WSL-Base
     kiwi_file: Fedora.kiwi
 execute: