Code review comment for lp:~smoser/maas-images/trunk.precise-squashfs

I've tested that it builds the squashfs image by:
  meph2-build -vv --config=conf/meph-v3.yaml amd64 precise \
     20180201 precise-server-cloudimg-amd64-root.tar.xz \
     precise-output.d/

The squashfs image will be generated in another way:
  using 'img2squashfs' from the last built image

Thus, *This change is not strictly necessary*.

However, it is good to have the maas-images code correctly
building the output if we ever needed to do that again.