Apply a naming rule of GET to show_server method

[GET /resources] methods should be "list_<resource name>s"
or "show_<resource name>", so this patch applies the rule
to show_server method of compute clients.

Partially implements blueprint consistent-service-method-names

Change-Id: I92addd2ad6502fe00395e2b9455de25c2f53d115
diff --git a/tempest/common/waiters.py b/tempest/common/waiters.py
index 249bac9..bdbd6bc 100644
--- a/tempest/common/waiters.py
+++ b/tempest/common/waiters.py
@@ -33,7 +33,7 @@
 
     # NOTE(afazekas): UNKNOWN status possible on ERROR
     # or in a very early stage.
-    body = client.get_server(server_id)
+    body = client.show_server(server_id)
     old_status = server_status = body['status']
     old_task_state = task_state = _get_task_state(body)
     start_time = int(time.time())
@@ -60,7 +60,7 @@
                 return
 
         time.sleep(client.build_interval)
-        body = client.get_server(server_id)
+        body = client.show_server(server_id)
         server_status = body['status']
         task_state = _get_task_state(body)
         if (server_status != old_status) or (task_state != old_task_state):