Add test case for force detach volume

V2 volumes_client in Tempest doesn't contain volume action: force
detach volume. This patch adds the support.

Including:

[1] Add force detach volume api to v2 volumes client
[2] Add release notes
[3] Add unit test for force detach volume api
[3] Add test case: test_force_detach_volume

Change-Id: I172913b7d372225328a3c30299926c599c7d245a
diff --git a/releasenotes/notes/add-force-detach-volume-to-volumes-client-library-b2071f2954f8e8b1.yaml b/releasenotes/notes/add-force-detach-volume-to-volumes-client-library-b2071f2954f8e8b1.yaml
new file mode 100644
index 0000000..a0156a0
--- /dev/null
+++ b/releasenotes/notes/add-force-detach-volume-to-volumes-client-library-b2071f2954f8e8b1.yaml
@@ -0,0 +1,6 @@
+---
+features:
+  - |
+    Add force detach volume feature API to v2 volumes_client library.
+    This feature enables the possibility to force a volume to detach, and
+    roll back an unsuccessful detach operation after you disconnect the volume.