Introduce an API test for specified floating ip address

The test case checks whether admin can set floating IP address when
creates a floating IP.
Implements: blueprint allow-specific-floating-ip-address[1]

[1] https://blueprints.launchpad.net/neutron/+spec/allow-specific-floating-ip-address

Change-Id: I036da37402b826c1a73698e0ae21894a3ce676ab
diff --git a/neutron/tests/tempest/config.py b/neutron/tests/tempest/config.py
index 200b247..4b35d92 100644
--- a/neutron/tests/tempest/config.py
+++ b/neutron/tests/tempest/config.py
@@ -480,6 +480,10 @@
                      "the extended IPv6 attributes ipv6_ra_mode "
                      "and ipv6_address_mode"
                 ),
+    cfg.BoolOpt('specify_floating_ip_address_available',
+                default=True,
+                help='Allow passing an IP Address of the floating ip when '
+                     'creating the floating ip'),
 ]
 
 messaging_group = cfg.OptGroup(name='messaging',