Handle instances without attached ports.

This change covers the case where an instance has no ports (addresses)
attached making the function network_name_from_instance() raise a
StopIteration since the "addresses" dict is empty.

Traceback (most recent call last):
  File "[...]/zaza/openstack/charm_tests/manila/tests.py", line 142, in tearDownClass
    fips_reservations += neutron_tests.floating_ips_from_instance(vm)
  File "[...[/zaza/openstack/charm_tests/neutron/tests.py", line 1028, in floating_ips_from_instance
    return ips_from_instance(instance, 'floating')
  File "[...]/zaza/openstack/charm_tests/neutron/tests.py", line 1073, in ips_from_instance
    network_name_from_instance(instance)]
  File "[...]/zaza/openstack/charm_tests/neutron/tests.py", line 1052, in network_name_from_instance
    return next(iter(instance.addresses))
StopIteration

Fixes #771

unit_tests/charm_tests/test_neutron.py

@@ -0,0 +1,50 @@
+# Copyright 2022 Canonical Ltd.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+import unittest
+
+import zaza.openstack.charm_tests.neutron.tests as neutron_tests
+
+
+class FakeInstance:
+    def __init__(self):
+        self.addresses = {
+            "foo_admin_net": [
+                {"addr": "10.5.1.2",
+                 "OS-EXT-IPS:type": "fixed"},
+                {"addr": "10.245.166.188",
+                 "OS-EXT-IPS:type": "floating"},
+            ]
+        }
+
+
+class TestNeutron(unittest.TestCase):
+    def test_network_name_from_instance(self):
+        instance = FakeInstance()
+
+        self.assertEqual('foo_admin_net',
+                         neutron_tests.network_name_from_instance(instance))
+
+        instance.addresses = {}
+        self.assertEqual(None,
+                         neutron_tests.network_name_from_instance(instance))
+
+    def  test_ips_from_instance(self):
+        instance = FakeInstance()
+        self.assertEqual(["10.245.166.188"],
+                         neutron_tests.ips_from_instance(instance, "floating"))
+        self.assertEqual(["10.5.1.2"],
+                         neutron_tests.ips_from_instance(instance, "fixed"))
+        instance.addresses = {}
+        self.assertEqual([],
+                         neutron_tests.ips_from_instance(instance, "floating"))

zaza/openstack/charm_tests/neutron/tests.py

@@ -1076,7 +1076,10 @@ def network_name_from_instance(instance):
     :returns: Name of primary network the instance is attached to.
     :rtype: str
     """
-    return next(iter(instance.addresses))
+    try:
+        return next(iter(instance.addresses))
+    except StopIteration:
+        return None
 
 
 def ips_from_instance(instance, ip_type):
@@ -1095,10 +1098,14 @@ def ips_from_instance(instance, ip_type):
         raise RuntimeError(
             "Only 'floating' and 'fixed' are valid IP types to search for"
         )
-    return list([
-        ip['addr'] for ip in instance.addresses[
-            network_name_from_instance(instance)]
-        if ip['OS-EXT-IPS:type'] == ip_type])
+    net_name = network_name_from_instance(instance)
+    if net_name:
+        return list([
+            ip['addr'] for ip in instance.addresses[net_name]
+            if ip['OS-EXT-IPS:type'] == ip_type])
+    else:
+        # the instance is not attached to a network.
+        return []
 
 
 class NeutronNetworkingTest(NeutronNetworkingBase):