Fix vs test issue: failed to remove vlan due to referenced by vlan interface (sonic-net#2504)

*Fix: remove vlan interface before removing the vlan itself

Author: stephenxs

tests/dvslib/dvs_vlan.py

@@ -46,6 +46,10 @@ def remove_vlan_member(self, vlanID, interface):
         member = "Vlan{}|{}".format(vlanID, interface)
         self.config_db.delete_entry("VLAN_MEMBER", member)
 
+    def remove_vlan_interface(self, vlanID):
+        vlan = "Vlan{}".format(vlanID)
+        self.config_db.delete_entry("VLAN_INTERFACE", vlan)
+
     def check_app_db_vlan_fields(self, fvs, admin_status="up", mtu="9100"):
         assert fvs.get("admin_status") == admin_status
         assert fvs.get("mtu") == mtu

tests/test_vlan.py

@@ -459,6 +459,7 @@ def arp_accept_disabled():
 
         wait_for_result(arp_accept_disabled, PollingConfig(), "IPv4 arp_accept not disabled")
 
+        self.dvs_vlan.remove_vlan_interface(vlan)
         self.dvs_vlan.remove_vlan(vlan)
         self.dvs_vlan.get_and_verify_vlan_ids(0)
 
@@ -487,6 +488,7 @@ def proxy_arp_disabled():
 
         wait_for_result(proxy_arp_disabled, PollingConfig(), 'IPv4 proxy_arp or proxy_arp_pvlan not disabled')
 
+        self.dvs_vlan.remove_vlan_interface(vlan)
         self.dvs_vlan.remove_vlan(vlan)
         self.dvs_vlan.get_and_verify_vlan_ids(0)