tests for configure edge gateways

Added tests for configuring edge gateway
- tests configure the firewall services. Adds a firewall rule for an
  not so important, unused port. This rule is by default disabled, so
should not break anything even if user runs it by mistake against a
firewall.
Tests reverts the data back to normal after run

These tests run both in mock and non-mock mode.
added comment on test
Merge pull request #2289 from alphagov/tests_for_edge_gateway

tests for configure edge gateways