Add tests for Share Network Subnet Metadata

Adds positive and negative tests for share network subnet metadata.
Works to microversion 2.78 and later.

Change-Id: I32268eaa16b6b56ef4dda32806983744809c8707
Depends-On: https://review.opendev.org/c/openstack/manila-tempest-plugin/+/877674
Signed-off-by: Kiran Pawar <kinpaa@gmail.com>
diff --git a/manila_tempest_tests/tests/api/base.py b/manila_tempest_tests/tests/api/base.py
index 9583de8..7e9e1c4 100644
--- a/manila_tempest_tests/tests/api/base.py
+++ b/manila_tempest_tests/tests/api/base.py
@@ -779,11 +779,12 @@
     def create_share_network_subnet(cls,
                                     client=None,
                                     cleanup_in_class=False,
+                                    metadata=None,
                                     **kwargs):
         if client is None:
             client = cls.shares_v2_client
         share_network_subnet = client.create_subnet(
-            **kwargs)['share_network_subnet']
+            metadata=metadata, **kwargs)['share_network_subnet']
         resource = {
             "type": "share_network_subnet",
             "id": share_network_subnet["id"],