Add options to use remove_unused_* parameters

Being able to modify the parameters "remove_unused_base_images",
"remove_unused_original_minimum_age_seconds",
"remove_unused_kernels", "remove_unused_resized_minimum_age_seconds"
if desired.

Change-Id: Ia24594ccc4b999674456e59a279e2d5916cd5d7a
Implements: blueprint add-remove-unused-parameters
Merge "Add options to use remove_unused_* parameters"