Use per character suffix for multi image

E.g. if you pull the oat files from the device, you get oat files
with the following names:
system@framework@boot.art

But the name stored in the image header is:
boot.art

So we need to append system@framework@ as a file name prefix to each
image file to get the actual one.

Required for adding oatdump support for app images.

Bug: 22858531
Bug: 27408512

Change-Id: I93dd3f16652400f232e6175670fcd572395879e0