Add test_ping_global_ip_from_vm_with_fip

We need such a test in order to be able to catch issues like [1].
The test creates network and server, then launches a VM with a FIP.
Then connects to the FIP and pings a global ip address.
The test requires global_ip_address variable in tempest.conf.
By default the value is not set and the test will be skipped.

[1] https://bugzilla.redhat.com/show_bug.cgi?id=1834433

Change-Id: Ibb3db814ed9b42f28ced8378368a3d5c2e43d7b3
diff --git a/neutron_tempest_plugin/config.py b/neutron_tempest_plugin/config.py
index 28d6b76..2290d0f 100644
--- a/neutron_tempest_plugin/config.py
+++ b/neutron_tempest_plugin/config.py
@@ -60,6 +60,10 @@
     cfg.IntOpt('max_mtu',
                default=1500,
                help='Max mtu value of default deployments".'),
+    cfg.StrOpt('global_ip_address',
+               default='',
+               help='An IP address in the Internet that can be used in '
+                    'a connectivity test'),
     cfg.StrOpt('q_agent',
                default=None,
                choices=['None', 'linuxbridge', 'ovs', 'sriov'],