Patch to fix test_rebuild_volume_backed_server

Test fails with "root" user, changed it to "cirros"

Related-prod: PRODX-43715
Change-Id: I99eabb280488d30cf9c80d5fe78804004672fb36
diff --git a/tempest/api/compute/servers/test_server_actions.py b/tempest/api/compute/servers/test_server_actions.py
index 10153bb..938e4b4 100644
--- a/tempest/api/compute/servers/test_server_actions.py
+++ b/tempest/api/compute/servers/test_server_actions.py
@@ -880,7 +880,7 @@
         # 4.Plain username/password auth, if a password was given.
         linux_client = remote_client.RemoteClient(
             self.get_server_ip(server, self.validation_resources),
-            self.ssh_user,
+            self.ssh_alt_user,
             password=None,
             pkey=self.validation_resources['keypair']['private_key'],
             server=server,
diff --git a/tempest/config.py b/tempest/config.py
index 5b54956..69b6b12 100644
--- a/tempest/config.py
+++ b/tempest/config.py
@@ -937,7 +937,7 @@
                default="root",
                help="User name used to authenticate to an instance."),
     cfg.StrOpt('image_alt_ssh_user',
-               default="root",
+               default="cirros",
                help="User name used to authenticate to an alt instance."),
     cfg.StrOpt('image_ssh_password',
                default="password",