Draft: .oniro-ci: use CI_ONIRO_RUNNER_EPHEMERAL_STORAGE

When the variable is defined it ought to point to ephemeral storage that is "better" than the default storage provided by the runner.

This may be, for example, memory-backed file system designed to seed things up and avoid wearing down persistent storage.

I've tested this with a local runner using 100GB tmpfs partition as ephemeral storage. Due to package accumulation that amount fills up to about 60GB for oniro-image-base x86-64 build.

With DEPLOY_DIR on separate non-ram filesystem, tmpfs usage is very good, easily allowing 2-4 concurrent builds on the same 100GB tmpfs.

Signed-off-by: Zygmunt Krynicki zygmunt.krynicki@huawei.com