OVS link: Implement OVS link plugin

OVS link: Implement OVS link plugin

This plugin consists of two parts:
 - OVS link
    The implementation of the plugin itself, which uses
    OVS utils API to be able to monitor a link status of
    OVS connected interfaces and dispatch the values
    through collectd notification mechanism whenever
    the link state change occurs.

 - OVS utils
    This module implements the OVS DB communication routine
    specified by RFC7047. It includes:
      - Connecting/disconnecting to/from OVS DB (via TCP/UNIX);
      - Mechanism to subscribe to OVS DB table events like
        init/insert/modify/delete table rows;
      - API to send custom request and receive result;
      - Recovery connection mechanism with OVS DB;
      - Handling of ECHO request to verify the liveness
        of a database connection;
      - Helpers functions.

Change-Id: Icac392bd1bd40f7dd156bfd2fc4ff08d9725a22f
Signed-off-by: Mytnyk, VolodymyrX <volodymyrx.mytnyk@intel.com>