Support creating emulator instance with --local-system-image

Acloud supports mixing emulator's images with a different system image
and creating a local instance. The setup requires a build for emulator,
a build for system image, and OTA tools.

Bug: 140786679
Test: python -m acloud.create.goldfish_local_image_local_instance_test
Test: python -m acloud.internal.lib.ota_tools_test
Test: acloud-dev create --avd-type goldfish \
      --local-image --local-instance \
      --local-system-image ~/generic_x86_gsi

Change-Id: Ie1cc8cd8613df2985823a787f13af1b3097e0f09
7 files changed