Add set-src-dest-host role

The role will find out the available hosts and set
compute.migration_source_host and compute.migration_dest_host
options in tempest.conf if tempest_set_src_dest_host is set to
True.

Change-Id: Ic01970b100a7bb30d9c78229204c7de67681108c
diff --git a/zuul.d/integrated-gate.yaml b/zuul.d/integrated-gate.yaml
index 4b4306c..8d2842e 100644
--- a/zuul.d/integrated-gate.yaml
+++ b/zuul.d/integrated-gate.yaml
@@ -263,6 +263,7 @@
       # requests to services and can cause more oom issues. To avoid the
       # oom issue, setting the concurrency to 4 in this job.
       tempest_concurrency: 4
+      tempest_set_src_dest_host: true
       devstack_localrc:
         USE_PYTHON3: true
       devstack_plugins: