The merge tool originally was meant to merge somewhat different things,
and thus this was helpful in the early versions. However, at this point
we want parameters to be more stable and we don't generally merge things
that have their own image parameter.
Meanwhile this feature caused problems as we change resource names.
This is a backward incompatible change of default behavior, but the old
behavior can be had again by passing --change-image-params.
Change-Id: I78cf31f0443f3d9f274758f5471a5bca9155635d
f9ef457987