Sort the file with image content.

While modifying the CTS shim apex packages, it was observed that the
output of the image content file is not necessarily sorted, which in
turn can cause failure when checking the file against a whitelist.

Bug: 138429615
Test: Succesfully built a modified version of CTS Shim v3 that was
previously failing because of the issue this CL fixes.

Change-Id: I901859ae08feb6012f34b851e125977e1c0100d9