start_docker_service is a coroutine that took docker_args and
image_args by const reference. Its caller start_fake_gcs_server
is a regular function that passes temporaries (initializer lists)
and immediately returns a future. The temporaries are destroyed
when the caller returns, leaving the coroutine holding dangling
references.
On the first loop iteration this works by luck (memory not yet
reused), but on retry (after "address already in use") the
params.append_range(image_args) reads freed memory, causing
use-after-free that manifests as std::bad_alloc or broken_promise
in non-sanitizer builds.
Fix by taking docker_args and image_args by value so the coroutine
frame owns the vectors for its entire lifetime.
Fixes: https://scylladb.atlassian.net/browse/SCYLLADB-2003Closesscylladb/scylladb#29932
Adds a wrapper for seastar::experimental::process, to help
use external process fixtures in unit test. Mainly to share
concepts such as line reading of stdout/err etc, and sync
the shutdown of these. Also adds a small path searcher to
find what you want to run.
