Test coverage improvement for FWaaS screens

This patch set adds 'delete' ans 'update_get' tests
for policies, rules and firewalls and removes some
redundant code from another tests.

Closes-Bug: #1274136

Change-Id: I5e00419621fd6aa14ec82a5a19887754e03c1d0e
Merge "Test coverage improvement for FWaaS screens"