ext4_utils: don't leave bad image file in case of error

Bug: 13029951
Change-Id: Ibe50a503c2d3988813b362790b7fba83383fb51e
Don't wipe when formatting ext4 for way faster zip flashing

Change-Id: Ib42337b5607bdab08a46ff1ee3eb4c04e684f9e5