This helps us to add a new mode to handle large APKs in the follow
up CL.
Changes include:
1. Create a new interface class 'Image'
1. Create subclasses 'ZipModeImage' and 'ImageModeImage' and move the
related functions there.
Bug: 63542719
Test: recovery_component_test passes
Change-Id: I7729b0ba39b19a9c84811636a60dd0a0b1acc2f0