Remove api_version setting from volume v3/v2 service client

Volume service clients has been made as generic without
api_version[1] so that catalog_type can select the appropriate
endpoint to make API request.

There are few service clients belonged to v3 still set
api_version which is not needed now.

This commit removes the api_version from volume service
clients completely.
[1] https://review.openstack.org/#/c/527889/

Related-prod: PRODX-9612
Change-Id: Iaf2d06b0f124e1c7b959785a04a4d770898a1eea
diff --git a/tempest/lib/services/volume/v3/backups_client.py b/tempest/lib/services/volume/v3/backups_client.py
index e742e39..b3f7ca8 100644
--- a/tempest/lib/services/volume/v3/backups_client.py
+++ b/tempest/lib/services/volume/v3/backups_client.py
@@ -21,7 +21,6 @@
 
 class BackupsClient(backups_client.BackupsClient):
     """Volume V3 Backups client"""
-    api_version = "v3"
 
     def update_backup(self, backup_id, **kwargs):
         """Updates the specified volume backup.
diff --git a/tempest/lib/services/volume/v3/base_client.py b/tempest/lib/services/volume/v3/base_client.py
index e78380b..617da2e 100644
--- a/tempest/lib/services/volume/v3/base_client.py
+++ b/tempest/lib/services/volume/v3/base_client.py
@@ -20,4 +20,3 @@
 
 BaseClient = moves.moved_class(base_client.BaseClient, 'BaseClient', __name__,
                                version="Pike", removal_version='?')
-BaseClient.api_version = 'v3'
diff --git a/tempest/lib/services/volume/v3/group_snapshots_client.py b/tempest/lib/services/volume/v3/group_snapshots_client.py
index 6e53e3e..16412d3 100644
--- a/tempest/lib/services/volume/v3/group_snapshots_client.py
+++ b/tempest/lib/services/volume/v3/group_snapshots_client.py
@@ -23,7 +23,6 @@
 
 class GroupSnapshotsClient(base_client.BaseClient):
     """Client class to send CRUD Volume Group Snapshot API requests"""
-    api_version = 'v3'
 
     def create_group_snapshot(self, **kwargs):
         """Creates a group snapshot.
diff --git a/tempest/lib/services/volume/v3/group_types_client.py b/tempest/lib/services/volume/v3/group_types_client.py
index ecbcba1..1ccb9f8 100644
--- a/tempest/lib/services/volume/v3/group_types_client.py
+++ b/tempest/lib/services/volume/v3/group_types_client.py
@@ -22,7 +22,6 @@
 
 class GroupTypesClient(base_client.BaseClient):
     """Client class to send CRUD Volume V3 Group Types API requests"""
-    api_version = 'v3'
 
     @property
     def resource_type(self):
diff --git a/tempest/lib/services/volume/v3/groups_client.py b/tempest/lib/services/volume/v3/groups_client.py
index e2e477d..3cf1e6a 100644
--- a/tempest/lib/services/volume/v3/groups_client.py
+++ b/tempest/lib/services/volume/v3/groups_client.py
@@ -23,7 +23,6 @@
 
 class GroupsClient(base_client.BaseClient):
     """Client class to send CRUD Volume Group API requests"""
-    api_version = 'v3'
 
     def create_group(self, **kwargs):
         """Creates a group.
diff --git a/tempest/lib/services/volume/v3/messages_client.py b/tempest/lib/services/volume/v3/messages_client.py
index 0127271..47538cd 100644
--- a/tempest/lib/services/volume/v3/messages_client.py
+++ b/tempest/lib/services/volume/v3/messages_client.py
@@ -22,7 +22,6 @@
 
 class MessagesClient(base_client.BaseClient):
     """Client class to send user messages API requests."""
-    api_version = 'v3'
 
     def show_message(self, message_id):
         """Show details for a single message."""
diff --git a/tempest/lib/services/volume/v3/snapshots_client.py b/tempest/lib/services/volume/v3/snapshots_client.py
index 88c094f..d55fe7e 100644
--- a/tempest/lib/services/volume/v3/snapshots_client.py
+++ b/tempest/lib/services/volume/v3/snapshots_client.py
@@ -18,4 +18,4 @@
 
 class SnapshotsClient(snapshots_client.SnapshotsClient):
     """Client class to send CRUD Volume Snapshot V3 API requests."""
-    api_version = "v3"
+    pass
diff --git a/tempest/lib/services/volume/v3/versions_client.py b/tempest/lib/services/volume/v3/versions_client.py
index 5702f95..57629bd 100644
--- a/tempest/lib/services/volume/v3/versions_client.py
+++ b/tempest/lib/services/volume/v3/versions_client.py
@@ -22,7 +22,6 @@
 
 
 class VersionsClient(base_client.BaseClient):
-    api_version = 'v3'
 
     def list_versions(self):
         """List API versions
diff --git a/tempest/lib/services/volume/v3/volumes_client.py b/tempest/lib/services/volume/v3/volumes_client.py
index 5f4b278..45fb8a5 100644
--- a/tempest/lib/services/volume/v3/volumes_client.py
+++ b/tempest/lib/services/volume/v3/volumes_client.py
@@ -22,7 +22,6 @@
 
 class VolumesClient(volumes_client.VolumesClient):
     """Client class to send CRUD Volume V3 API requests"""
-    api_version = "v3"
 
     def show_volume_summary(self, **params):
         """Get volumes summary.