Rectify test of bgp l3vpn

Related-Bug: PRODX-11809
Change-Id: Ifa2f905000a4e8123e7905af4faa8fc94d1ee064
diff --git a/neutron_tempest_plugin/bgpvpn/scenario/test_bgpvpn_advanced.py b/neutron_tempest_plugin/bgpvpn/scenario/test_bgpvpn_advanced.py
index d4fe6d3..ed8abe0 100644
--- a/neutron_tempest_plugin/bgpvpn/scenario/test_bgpvpn_advanced.py
+++ b/neutron_tempest_plugin/bgpvpn/scenario/test_bgpvpn_advanced.py
@@ -86,7 +86,8 @@
         """
 
         self._create_networks_and_subnets(
-            subnet_cidr=CONF.bgpvpn.l3vpn_endpoint
+            subnet_cidr=CONF.bgpvpn.l3vpn_private_subnet,
+            reserve_ip_address=False,
         )
         self._create_server()
         self._create_bgpvpn(rts=CONF.bgpvpn.route_target)
@@ -96,7 +97,11 @@
         )
 
     def _create_networks_and_subnets(
-        self, name="bgp", subnet_cidr=None, port_security=True
+        self,
+        name="bgp",
+        subnet_cidr=None,
+        port_security=True,
+        reserve_ip_address=True,
     ):
         self.network = self._create_network(
             namestart=name, port_security_enabled=port_security
@@ -104,7 +109,10 @@
         self.subnet = self._create_subnet_with_cidr(
             self.network, cidr=subnet_cidr, ip_version=4
         )
-        self._reserve_ip_address(subnet_cidr.split("/")[0], self.os_primary)
+        if reserve_ip_address:
+            self._reserve_ip_address(
+                subnet_cidr.split("/")[0], self.os_primary
+            )
 
     def _create_subnet_with_cidr(
         self, network, subnets_client=None, namestart="subnet-bgp", **kwargs
diff --git a/neutron_tempest_plugin/config.py b/neutron_tempest_plugin/config.py
index 9917817..bac18f9 100644
--- a/neutron_tempest_plugin/config.py
+++ b/neutron_tempest_plugin/config.py
@@ -165,6 +165,10 @@
                default=200,
                help=("Maximum number for the range of "
                      "assigned number for distinguishers.")),
+    cfg.StrOpt('l3vpn_private_subnet',
+               default='10.22.0.0/24',
+               help=("IP Address/Mask of instance, which will be "
+                     "used to test the l3vpn connectivity.")),
     cfg.StrOpt('l3vpn_endpoint',
                default=None,
                help=("IP Address/Mask, which will be used to "