Add option for whether the cloud supports floating ips

This commit adds a new config option to specify whether the cloud under
test supports floating ips or not. Not every cloud supports floating ips
so we need to be able to handle that and properly skip tests.

Change-Id: Iedc3c7f9d045408f54d94c34b478fb1b28b593c9
Closes-Bug: #1603492
diff --git a/tempest/api/compute/servers/test_server_rescue.py b/tempest/api/compute/servers/test_server_rescue.py
index 83151b3..b0ef3bc 100644
--- a/tempest/api/compute/servers/test_server_rescue.py
+++ b/tempest/api/compute/servers/test_server_rescue.py
@@ -65,6 +65,8 @@
     @decorators.idempotent_id('4842e0cf-e87d-4d9d-b61f-f4791da3cacc')
     @testtools.skipUnless(CONF.network.public_network_id,
                           'The public_network_id option must be specified.')
+    @testtools.skipUnless(CONF.network_feature_enabled.floating_ips,
+                          "Floating ips are not available")
     def test_rescued_vm_associate_dissociate_floating_ip(self):
         # Association of floating IP to a rescued vm
         floating_ip_body = self.floating_ips_client.create_floating_ip(