Resolve diamond shaped inheritance

In the previous implementation `firewall.AccessList` would inherit from
`l3.AccessList` which inherited from `base.Base`.
`firewall.AccessList` also inherited from
`firewall.FirewallPolicyObject`. That lead to a Diamond Shaped
inheritance. The fact that `FirewallPolicyObject` and `l3.AccessList`
had constructors with different arguments made it difficult to let
`super()` call the constructors with different arguments.

To resolve that, the diamond Shaped inheritance was resolved making it
clearer which `__init__`'s `super()` calls which superclasses
constructor.

The different signatures of the constructor still pose a problem, hence
we send all supplemental arguments of a constructor to `**kwargs`.

asr1k_neutron_l3/models/neutron/l3/access_list.py

@@ -20,10 +20,7 @@
 
 class AccessList(base.Base):
     def __init__(self, id, drop_on_17_3=False):
-        # If we use super(AccessList, self) here the MRO of type(self) is determining the __init__
-        # we call. If self is a child, that could lead to not calling base.Base.__init__().
-        # If the second argument to super is a type, the returned method is unbound, hence we pass self to it.
-        super(AccessList, AccessList).__init__(self)
+        super().__init__()
         self.id = id
         self._drop_on_17_3 = drop_on_17_3
         self.rules = []

asr1k_neutron_l3/models/neutron/l3/base.py

@@ -22,7 +22,7 @@
 
 
 class Base(object):
-    def __init__(self):
+    def __init__(self, **kwargs):
         self.contexts = asr1k_pair.ASR1KPair().contexts
 
     @property

asr1k_neutron_l3/models/neutron/l3/firewall.py

@@ -33,23 +33,23 @@
 LOG = logging.getLogger(__name__)
 
 
-class FirewallPolicyObject(base.Base):
+class FirewallPolicyMixin:
 
     PREFIX = None
 
     @classmethod
     def get_id_by_policy_id(cls, policy_id: str) -> str:
         if not cls.PREFIX:
-            raise NotImplementedError("Class derived from 'FirewallPolicyObject' must define static var 'PREFIX'")
+            raise NotImplementedError("Class derived from 'FirewallPolicyMixin' must define static var 'PREFIX'")
         return f"{cls.PREFIX}{policy_id}"
 
-    def __init__(self, policy_id: str):
+    def __init__(self, policy_id=None, **kwargs):
         self.policy_id = policy_id
         self.id = self.get_id_by_policy_id(self.policy_id)
-        super().__init__()
+        super().__init__(id=self.id, **kwargs)
 
 
-class AccessList(access_list.AccessList, FirewallPolicyObject):
+class AccessList(FirewallPolicyMixin, access_list.AccessList):
 
     PREFIX = const.FWAAS_ACL_PREFIX
     ACTIONS = {
@@ -98,7 +98,7 @@ def __init__(self, policy_id: str, rules: List[dict]):
             self.rules.append(access_list.Rule(**rule_args))
 
 
-class ClassMap(FirewallPolicyObject):
+class ClassMap(FirewallPolicyMixin, base.Base):
     PREFIX = const.FWAAS_CLASS_MAP_PREFIX
 
     @property
@@ -107,7 +107,7 @@ def _rest_definition(self):
                           type='inspect', prematch='match-all')
 
 
-class ServicePolicy(FirewallPolicyObject):
+class ServicePolicy(FirewallPolicyMixin, base.Base):
     PREFIX = const.FWAAS_SERVICE_POLICY_PREFIX
 
     @property