Add missing attachments schema in servers.py

The following schemas are missing in servers.py in 2.71 and 2.73
  * attach_volume
  * show_volume_attachment
  * list_volume_attachments
This is to add them.

Change-Id: Ic8375425c712992b09ebaea8f064ab03b95ff602
diff --git a/tempest/lib/api_schema/response/compute/v2_71/servers.py b/tempest/lib/api_schema/response/compute/v2_71/servers.py
index 5cf0f8a..f4c01ee 100644
--- a/tempest/lib/api_schema/response/compute/v2_71/servers.py
+++ b/tempest/lib/api_schema/response/compute/v2_71/servers.py
@@ -79,3 +79,6 @@
 check_tag_existence = copy.deepcopy(servers270.check_tag_existence)
 update_tag = copy.deepcopy(servers270.update_tag)
 delete_tag = copy.deepcopy(servers270.delete_tag)
+attach_volume = copy.deepcopy(servers270.attach_volume)
+show_volume_attachment = copy.deepcopy(servers270.show_volume_attachment)
+list_volume_attachments = copy.deepcopy(servers270.list_volume_attachments)
diff --git a/tempest/lib/api_schema/response/compute/v2_73/servers.py b/tempest/lib/api_schema/response/compute/v2_73/servers.py
index 6e491e9..ae7ebc4 100644
--- a/tempest/lib/api_schema/response/compute/v2_73/servers.py
+++ b/tempest/lib/api_schema/response/compute/v2_73/servers.py
@@ -76,3 +76,6 @@
 check_tag_existence = copy.deepcopy(servers271.check_tag_existence)
 update_tag = copy.deepcopy(servers271.update_tag)
 delete_tag = copy.deepcopy(servers271.delete_tag)
+attach_volume = copy.deepcopy(servers271.attach_volume)
+show_volume_attachment = copy.deepcopy(servers271.show_volume_attachment)
+list_volume_attachments = copy.deepcopy(servers271.list_volume_attachments)