Scrape the object store WAL metrics before stopping a cell's server whether
the load succeeded or failed, so failed cells keep their stall, poison and
create failure counters. Build the summary from the plan so that cells which
never ran are listed and leave their ratios undefined. Move budget, region,
runtime image, manifest and credential scan logic from the workflow into the
helper scripts, and drive the cell lifecycle in the tests through fake docker
and curl binaries.
Signed-off-by: jeremyhi <fengjiachun@gmail.com>