use pbnjson in debug_methods and subscription

:Release Notes:
Use pbnjson library to process debug methods and subscription

:Detailed Notes:
- replace cjson with pbnjson in debug_methods and subscription
- re-order, space strip in tests that expects exact string output of
  JSON generation.
- in unit-test /luna-service2/LSSubscriptionGetJson solidus slash
  escaping were removed because yajl refers to fact that it is optional
  and doesn't put back-slash escape before that character during JSON
  generation.

:Testing Performed:
unit-tests on desktop build

:QA Notes:

:Issues Addressed:
[BHV-6] luna-service2: replace cjson use with pbnjson

Open-webOS-DCO-1.0-Signed-off-by: Nikolay Orliuk <nikolay.orliuk@lge.com>

Change-Id: Ifbc861827e6fa0ec544ce55424481044bc7ad40e
Reviewed-on: https://g2g.palm.com/4871
Reviewed-by: DCO Verification
Reviewed-by: Anatolii Sakhnik <anatolii.sakhnik@lge.com>
Tested-by: Anatolii Sakhnik <anatolii.sakhnik@lge.com>