Fixes#25084
Add slirp4netns and use for nested containers. This will allow nested container port aliasing, helping CI stability.
Note: this contains and updated Dockerfile for dbuild image, but since chicken and eggs, right now will force install slirp4netns before anything in dbuild script.
Updates the mock server handling to use ephemeral ports and query from container, ensuring we don't get port collisions. (boost as well as pytest).
Includes a timeout up, and a tweak to our scylla_cluster handling, ensuring we don't deadlock when pipe size is less than requires for our sys notify messages.
Closesscylladb/scylladb#28727
* github.com:scylladb/scylladb:
gcs_fixture: Change to use docker helper
aws_kms_fixture: Modify to use docker helper
test/lib/proc_util: Add docker helper
pytest: use ephemeral port publish for docker mock servers
dbuild: Use container network in dbuild nested containers
scylla_cluster: Read notify sock in background to prevent deadlock
b228eb26e6