Use service_available option to detect Neutron

... because nova-network was removed in Ussuri release.

To run basic neutron tests by default, the default value of
[service_available] neutron option is changed to True.

Change-Id: I74cc344a9c1ae2aa523af754d22392869ff059f5

releasenotes/notes/enable-neutron-by-default-57b87a20acc1ac47.yaml

@@ -0,0 +1,9 @@
+---
+upgrade:
+  - |
+    Default value of the ``[service_available] neutron`` option has been
+    updated from ``False`` to ``True``.
+
+  - |
+    All tests which require network features are now skipped when
+    the ``[service_available] neutron`` option is set to ``False``

tempest/common/utils/__init__.py

@@ -29,12 +29,7 @@ def get_service_list():
         'compute': CONF.service_available.nova,
         'image': CONF.service_available.glance,
         'volume': CONF.service_available.cinder,
-        # NOTE(masayukig): We have two network services which are neutron and
-        # nova-network. And we have no way to know whether nova-network is
-        # available or not. After the pending removal of nova-network from
-        # nova, we can treat the network/neutron case in the same manner as
-        # the other services.
-        'network': True,
+        'network': CONF.service_available.neutron,
         # NOTE(masayukig): Tempest tests always require the identity service.
         # So we should set this True here.
         'identity': True,

tempest/config.py

@@ -1196,7 +1196,7 @@ ServiceAvailableGroup = [
                 default=True,
                 help="Whether or not cinder is expected to be available"),
     cfg.BoolOpt('neutron',
-                default=False,
+                default=True,
                 help="Whether or not neutron is expected to be available"),
     cfg.BoolOpt('glance',
                 default=True,