Fallback to creds provider for fixed IP network if no network_for_ssh

When using fixed IPs for ssh and dynamic credentials and
network tenant isolation, if network_for_ssh is not set
attempt to just lookup the proper address to use from the
server using the network resource that's stashed in the
credentials provider.

Change-Id: I045bdf6a8e3b22293a3c804538aed7c75cb36180
Closes-Bug: #1611100
diff --git a/tempest/scenario/manager.py b/tempest/scenario/manager.py
index 952c0c2..1547bcf 100644
--- a/tempest/scenario/manager.py
+++ b/tempest/scenario/manager.py
@@ -665,9 +665,20 @@
             # method is creating the floating IP there.
             return self.create_floating_ip(server)['ip']
         elif CONF.validation.connect_method == 'fixed':
-            addresses = server['addresses'][CONF.validation.network_for_ssh]
+            # Determine the network name to look for based on config or creds
+            # provider network resources.
+            if CONF.validation.network_for_ssh:
+                addresses = server['addresses'][
+                    CONF.validation.network_for_ssh]
+            else:
+                creds_provider = self._get_credentials_provider()
+                net_creds = creds_provider.get_primary_creds()
+                network = getattr(net_creds, 'network', None)
+                addresses = (server['addresses'][network['name']]
+                             if network else [])
             for address in addresses:
-                if address['version'] == CONF.validation.ip_version_for_ssh:
+                if (address['version'] == CONF.validation.ip_version_for_ssh
+                        and address['OS-EXT-IPS:type'] == 'fixed'):
                     return address['addr']
             raise exceptions.ServerUnreachable(server_id=server['id'])
         else: