Added support for pre_dbe_create and resource exhaustion error

partial-jira-bug: CEM-15158

1. AE-IDs can not be allocated during pre_dbe_create of VPG
   as the existing infra creates refs internally
   so added an exception when PI refs are sent along during
   VPG create. VPG must be created before adding PIs to them
2. Added Resource Exhaustion exception when more than
   supported AE-IDs are requested
3. Added UTs for all these usecases

Change-Id: Id0132b3f05b8bd5b85ff7dd4174945055875d3b2

src/config/api-server/vnc_cfg_api_server/resources/virtual_port_group.py

@@ -6,6 +6,7 @@
 
 from cfgm_common.exceptions import HttpError
 from cfgm_common.exceptions import NoIdError
+from cfgm_common.exceptions import ResourceExhaustionError
 from pysandesh.gen_py.sandesh.ttypes import SandeshLevel
 from vnc_api.gen.resource_common import VirtualPortGroup
 from vnc_api.gen.resource_xsd import VpgInterfaceParametersType
@@ -39,15 +40,21 @@ def _notify_ae_id_modified(cls, obj_dict=None, notify=False):
 
     @classmethod
     def _alloc_ae_id(cls, prouter_name, vpg_name):
-        pi_ae = cls.vnc_zk_client.alloc_ae_id(prouter_name, vpg_name)
+        try:
+            pi_ae = cls.vnc_zk_client.alloc_ae_id(prouter_name, vpg_name)
+        except ResourceExhaustionError as exc:
+            err_msg = ('ResourceExhaustionError: when allocating AE-ID for '
+                       'virtual-port-group (%s) at physical-router (%s)' % (
+                       vpg_name, prouter_name))
+            return False, (400, err_msg)
         attr_obj = VpgInterfaceParametersType(pi_ae)
         attr_dict = attr_obj.__dict__
         alloc_dict = {
             'ae_id': pi_ae,
             'prouter_name': prouter_name,
             'vpg_name': vpg_name,
         }
-        return attr_dict, alloc_dict
+        return True, (attr_dict, alloc_dict)
 
     @classmethod
     def _dealloc_ae_id(cls, prouter_name, ae_id, vpg_name):
@@ -108,7 +115,10 @@ def _process_alloc_ae_id(cls, db_obj_dict, vpg_name, obj_dict=None):
             pi_ae = db_pr_dict.get(pi_pr)
             if pi_ae is None:
                 # allocate
-                attr_dict, _alloc_dict = cls._alloc_ae_id(pi_pr, vpg_name)
+                ok, result = cls._alloc_ae_id(pi_pr, vpg_name)
+                if not ok:
+                    return ok, result
+                attr_dict, _alloc_dict = result
                 alloc_dealloc_dict['allocated_ae_id'].append(_alloc_dict)
                 msg = "Allocating AE-ID(%s) for PI(%s) at VPG(%s)/PR(%s)" % (
                     attr_dict, pi_uuid, vpg_name, pi_pr)
@@ -122,7 +132,10 @@ def _process_alloc_ae_id(cls, db_obj_dict, vpg_name, obj_dict=None):
                 if (db_pi_dict.values()[0] != curr_pi_dict.get(create_pi_uuids[0])):
                     # allocate a new ae-id as it belongs to different PR
                     db_pr = db_pi_dict.values()[0]
-                    attr_dict_leftover_pi, _alloc_dict = cls._alloc_ae_id(db_pr, vpg_name)
+                    ok, result = cls._alloc_ae_id(db_pr, vpg_name)
+                    if not ok:
+                        return ok, result
+                    attr_dict_leftover_pi, _alloc_dict = result
                     alloc_dealloc_dict['allocated_ae_id'].append(_alloc_dict)
                     msg = "Allocating AE-ID(%s) for PI(%s) at VPG(%s)/PR(%s)" % (
                         attr_dict_leftover_pi, db_pi_uuid, vpg_name, db_pr)
@@ -298,7 +311,7 @@ def update_physical_intf_type(cls, obj_dict=None,
     # end update_physical_intf_type
 
     @classmethod
-    def pre_dbe_create(cls, tenant_name, obj_dict, db_conn):
+    def pre_dbe_create(cls, tenant_name, obj_dict, db_conn, **kwargs):
         ret_val = ''
         if ('vpg-internal' in obj_dict['fq_name'][2] and
                 obj_dict.get('virtual_port_group_user_created', True)):