Bug 7142 - all VpnPortIpToPort entries are lost from ODL cache after

Bug 7142 - all VpnPortIpToPort entries are lost from ODL cache after
reboot.

As part of this fix we ensure that control path information mapping
a vpn to fixed-neutron-port (gleaned from openstack configuration by
the tenant) is persistently retained inside Config Datastore and so
it will be accessible immediately after ODL cluster reboot.

In addition to that we created a new Operational DS that will
hold discovered IPs from the cloud. In more detail, this review
encompasses:

1. Create a new LearntVpnVipToPort OPERATIONAL Datastore which
will contain discovered IP addresses via GARP/ARP responses.

2. The existing NeutronVpnPortIpToPort will be changed as a pure Config
only Datastore as it will store all Neutron Port and their IP and
MAC Addresses.  This datastore will continue to be used
for lookup during ARP resolution and SubnetRoute handling.

3. Decoupling of the mymac changes(subnetMac) from Arp cache feature.
Mymac changes would still be listening to the VpnPortipToPort DS.

4. The ArpNotificationHandler would now modify the LearntVpnVipToPort DS which
the ArpMonitoringHandler would listen to.

The feature which initiates periodic ARP-based location discovery of
non-neutron IPs from the controller brought in via the earlier review
here: https://git.opendaylight.org/gerrit/#/c/45410/

Co-Authored-By: Vivekanandan Narasimhan <n.vivekanandan@ericsson.com>
Change-Id: Ic96517f4a57fe547d42495274a74ec5aa32b7d9e
Signed-off-by: Gobinath <gobinath@ericsson.com>
Signed-off-by: Vivekanandan Narasimhan <n.vivekanandan@ericsson.com>