Refactor VTN Manager.

  * Associate MAC address with virtual mapping which maps the address
    in the MAC address table.
  * Associate ingress and egress flow entries with virtual mappings
    which map them in the flow database.
  * Enable to get source and destination hosts configured in flow entries
    for internal use.
  * Optimize the way to purge obsolete flow entries and MAC addresses.
  * Scan TopoEdgeUpdate list only one time when an edge update event
    is received.

Change-Id: Idecfe40d949616523f7036d72641afed3a7ecb8e
Signed-off-by: Shigeru Yasuda <s-yasuda@da.jp.nec.com>
Merge "Refactor VTN Manager."