Find goldfish images in subdirectory in SDK repo

Acloud finds goldfish images in the subdirectory if the local image
directory looks like an unzipped SDK repository package. It is
convenient for the users who download SDK repo from the build server.

Test: acloud-dev create --local-instance --avd-type goldfish \
      --local-image /tmp/sdk-repo-linux-system-images/
Bug: 153420299
Change-Id: I41f9ebcbde3d85e8538653bfc7fbd5050f40733a
2 files changed