Multiple fixes in various modules

Multiple fixes in various modules

This review includes following fixes or changes:

1> BGPManager using the batching infrastructure
to batch and apply VRFEntries to Config DS.
(both bgp advertisement and bgp withdrawals).

2> FibManager using the batching infrastructure
to batch and apply flow rules to Inventory Config DS.

3> VPN Refactoring - Concurrency for VPNInterfaceManager

4> Changed the code in dhcpservice such that we add only
direct and macvtap vnic_type to the neutron port cache.

5> Fix for bgp display commands to work in COMCLI

Change-Id: Ib0c0e8515f61e299fa49ef3d432232ce4f3313d7
Signed-off-by: Suraj Ranjan <suraj.ranjan@ericsson.com>