blueprint for 4.6.0 policy-handler active-passive

blueprint for 4.6.0 policy-handler active-passive

DCAEGEN2-932:
- mode_of_operation: active or passive
  = active is as before this change
  = in passive mode the policy-handler
    * closes the web-socket to PDP
    * skips the periodic catch_ups
    * still periodically checks for reconfigure
    * still allows usig the web-server to retrieve policies from PDP
- default is active

- when mode_of_operation changes from passive to active,
  the policy-handler invokes the catch_up right away

- config-kv contains the optional override field mode_of_operation
  = changing the mode_of_operation in config-kv and invoking
    POST /reconfigure will bring the new value and change the
    mode of operation of the policy-handler if no service_activator
    section is provided in consul-kv record

- reduced the default web-socket ping interval from 180 to 30
  seconds because PDP changed its default timeout on the web-socket
  from 400 seconds to 50 seconds

Change-Id: Iae93746336a38af4248a1c77fdcf98e31ce956bd
Signed-off-by: Alex Shatov <alexs@att.com>
Issue-ID: DCAEGEN2-932