Fix image dict synthesis with productmd 1.20
The changes to SUPPORTED_IMAGE_TYPES and SUPPORTED_IMAGE_FORMATS
in productmd 1.20 (including one straight-up typo...) break our
magic synthesis for pre-Pungi 4 images in various ways. This
should hopefully fix them all; at least it fixes the tests.
Signed-off-by: Adam Williamson <awilliam@redhat.com>