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>
4 files changed