Change the return type of GetImageArtifactsPath

This commit refactors the code without changing the functionality.
The function returns a named tuple. Optional fields will be added to the
tuple when local cuttlefish instances support mixed images.

Test: acloud-dev create --local-instance --local-image
Test: acloud-dev create --local-instance --build-id 7050048 \
      --build-target aosp_cf_x86_64_phone-userdebug
Bug: 176270532
Change-Id: I2443b2de5161b2fede9dba0dd6adfe4db937ef50
4 files changed