fix a minor bug when detecting server image flavor

* The function _detect_server_image_flavor has a parameter 'server_id',
* but does not use it (instead, it uses server_id of the class)

Change-Id: I94d46877a67c79035e4ecf3da9abc0156803f2b3
diff --git a/tempest/api/compute/servers/test_server_actions.py b/tempest/api/compute/servers/test_server_actions.py
index d985d2b..c090308 100644
--- a/tempest/api/compute/servers/test_server_actions.py
+++ b/tempest/api/compute/servers/test_server_actions.py
@@ -174,7 +174,7 @@
 
     def _detect_server_image_flavor(self, server_id):
         # Detects the current server image flavor ref.
-        resp, server = self.client.get_server(self.server_id)
+        resp, server = self.client.get_server(server_id)
         current_flavor = server['flavor']['id']
         new_flavor_ref = self.flavor_ref_alt \
             if current_flavor == self.flavor_ref else self.flavor_ref
diff --git a/tempest/api/compute/v3/servers/test_server_actions.py b/tempest/api/compute/v3/servers/test_server_actions.py
index 602bd5b..7eeb6ae 100644
--- a/tempest/api/compute/v3/servers/test_server_actions.py
+++ b/tempest/api/compute/v3/servers/test_server_actions.py
@@ -174,7 +174,7 @@
 
     def _detect_server_image_flavor(self, server_id):
         # Detects the current server image flavor ref.
-        resp, server = self.client.get_server(self.server_id)
+        resp, server = self.client.get_server(server_id)
         current_flavor = server['flavor']['id']
         new_flavor_ref = self.flavor_ref_alt \
             if current_flavor == self.flavor_ref else self.flavor_ref