Convert build_api and download_dir to attributes of remote host GF device factory

This commit converts build_api and download_dir from method arguments to
attributes. They are initialized when first used. The device factory
will not need to authenticate the client or create the download
directory in local image mode.

Test: python3 -m acloud.public.actions.remote_host_gf_device_factory_test
Bug: 245226952
Change-Id: Ifdb8a65fcab3b06996cb085208dcb00eb298c0b5
2 files changed