migration: Add qtest for migration over RDMA

migration: Add qtest for migration over RDMA

This qtest requires there is a RDMA(RoCE) link in the host.
In order to make the test work smoothly, introduce a
scripts/rdma-migration-helper.sh to detect existing RoCE link before
running the test.

Test will be skipped if there is no available RoCE link.
 # Start of rdma tests
 # Running /x86_64/migration/precopy/rdma/plain
 ok 1 /x86_64/migration/precopy/rdma/plain # SKIP No rdma link available
 # To enable the test:
 # Run 'scripts/rdma-migration-helper.sh setup' with root to setup a new rdma/rxe link and rerun the test
 # Optional: run 'scripts/rdma-migration-helper.sh clean' to revert the 'setup'

 # End of rdma tests

Cc: Philippe Mathieu-Daudé <philmd@linaro.org>
Cc: Stefan Hajnoczi <stefanha@gmail.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
Message-ID: <20250311024221.363421-1-lizhijian@fujitsu.com>
[add 'head -1' to script, reformat test message]
Signed-off-by: Fabiano Rosas <farosas@suse.de>