tests/migration: parse the thread-id key of CpuInfoFast

thread_id in CpuInfoFast is deprecated, parse thread-id instead
after execute qmp query-cpus-fast. fix this so that test can
go smoothly.

Signed-off-by: Hyman Huang(黄勇) <huangy81@chinatelecom.cn>
Message-Id: <584578c0a0dd781cee45f72ddf517f6e6a41c504.1622729934.git.huangy81@chinatelecom.cn>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

tests/migration/guestperf/engine.py

@@ -113,7 +113,7 @@ def _migrate(self, hardware, scenario, src, dst, connect_uri):
         vcpus = src.command("query-cpus-fast")
         src_threads = []
         for vcpu in vcpus:
-            src_threads.append(vcpu["thread_id"])
+            src_threads.append(vcpu["thread-id"])
 
         # XXX how to get dst timings on remote host ?