Fix scenario base functions

There were two issues introduced in [1] which are fixed here:

- Calling create_server() with parameter security_groups=None fails,
  we need to use the "default" group instead of passing "None" to nova.
- The signature of create_secgroup_rules() was changed, we need to
  append the new parameter at the end in order to preserve
  compatibility with existing callers.

[1] I711a10eef321622c335e35b84e386b01d73b938a
Change-Id: I506dfa66378a9c7c59e2296f35f88613a1bd3af1
diff --git a/neutron_tempest_plugin/scenario/base.py b/neutron_tempest_plugin/scenario/base.py
index 9fe6a94..50f6b54 100644
--- a/neutron_tempest_plugin/scenario/base.py
+++ b/neutron_tempest_plugin/scenario/base.py
@@ -77,8 +77,9 @@
         """
 
         name = kwargs.get('name', data_utils.rand_name('server-test'))
-        security_groups = kwargs.get(
-            'security_groups', [{'name': 'default'}])
+        security_groups = kwargs.get('security_groups')
+        if not security_groups:
+            security_groups = [{'name': 'default'}]
         availability_zone = kwargs.get('availability_zone')
 
         server_args = {
@@ -119,8 +120,8 @@
         return body['keypair']
 
     @classmethod
-    def create_secgroup_rules(cls, rule_list, client=None,
-                              secgroup_id=None):
+    def create_secgroup_rules(cls, rule_list, secgroup_id=None,
+                              client=None):
         client = client or cls.os_primary.network_client
         if not secgroup_id:
             sgs = client.list_security_groups()['security_groups']
@@ -153,7 +154,7 @@
                       'port_range_max': 22,
                       'remote_ip_prefix': '0.0.0.0/0'}]
         client = client or cls.os_primary.network_client
-        cls.create_secgroup_rules(rule_list, client,
+        cls.create_secgroup_rules(rule_list, client=client,
                                   secgroup_id=secgroup_id)
 
     @classmethod
@@ -168,7 +169,7 @@
                       'port_range_max': 0,  # code
                       'remote_ip_prefix': '0.0.0.0/0'}]
         client = client or cls.os_primary.network_client
-        cls.create_secgroup_rules(rule_list, client,
+        cls.create_secgroup_rules(rule_list, client=client,
                                   secgroup_id=secgroup_id)
 
     @classmethod