Handle no more IP addresses available during a network sync

In some corner cases, like when db_sync is performed after OVS to OVN
migration, an implicit metadata port creation on a network with
depleted IP pool can raise IP allocation error. Just catch and log
this error such that the db_sync tool can finish syncing.

Change-Id: Ibb32ec5492c4fe00b9dac510f7e69160982992dd
(cherry picked from commit a86e300)

Author: mtomaska

neutron/plugins/ml2/drivers/ovn/mech_driver/ovsdb/ovn_db_sync.py

@@ -1028,6 +1028,10 @@ def sync_networks_ports_and_dhcp_opts(self, ctx):
                 except RuntimeError:
                     LOG.warning("Create network in OVN NB failed for "
                                 "network %s", network['id'])
+                except n_exc.IpAddressGenerationFailure:
+                    LOG.warning("No more IP addresses available during "
+                                "implicit port creation while creating "
+                                "network %s", network['id'])
 
         self._sync_metadata_ports(ctx, db_ports)