[Toaster] [review-request version2] remove custom images from Image Recipes page

[Dave Lerner]

Branch: master
Defect: bz9111
Summary: don't show custom images on Configuration | Image Recipes page

Tests
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Create custom image xxxxx based on core-image-minimal and build it.
View Image Recipes page.
Verify that core-image-minimal is in the list and 
    verify that xxxxx is not in the list.

View custom image page.
Verify that xxxxx *is* in the list.