Use _parse_resp method from tempest

As a continuation of the patch [1]. The required change
was merged in tempest. So we can make the cleanup in
manila_tempest_plugin.

[1] https://review.opendev.org/c/openstack/manila-tempest-plugin/+/836877

Change-Id: I093be875910ef18deebe3e56b83c6992d1a307e5
2 files changed