Do not consider subnets of shared public nets

Test test_external_network_visibility in
tempest.api.network.test_network fails when running
tempest against a deployment with public networks which
are shared among non-admin tenants.

This patch skips the public networks whose shared
property is set to true, as their subnets will be visible to
non-admin tenants.

Change-Id: Ieafb8e4094e603e259d68c4f485194a602dfc0cf
Closes-Bug: #1425962
diff --git a/tempest/api/network/test_networks.py b/tempest/api/network/test_networks.py
index 5e3e374..7a96f34 100644
--- a/tempest/api/network/test_networks.py
+++ b/tempest/api/network/test_networks.py
@@ -393,7 +393,9 @@
                                       " in filtered list (%s)." % nonexternal)
         self.assertIn(CONF.network.public_network_id, networks)
 
-        subnets_iter = (network['subnets'] for network in body['networks'])
+        subnets_iter = (network['subnets']
+                        for network in body['networks']
+                        if not network['shared'])
         # subnets_iter is a list (iterator) of lists. This flattens it to a
         # list of UUIDs
         public_subnets_iter = itertools.chain(*subnets_iter)