1. Restructure vcenter monitor code to create 3 classes:
   a. VCenterDB to populate info from VMware/VCenter
   b. VncDB to populate/add/delete info from Contrail VNC
   c. VCenterMonitor to sync the virtual network, virtual machine,
      and virtual machine interface information
2. Add code to give plug and unplug notification to VRouter. The
   VRouter IP is stored in the virtual machine display name in VNC.
3. Change ContrailVRouterApi to support one shot mode of operation
   by not calling Connect.

Change-Id: I3cc65fedb180dce0d77c0183ffe9b9edb324c4c4