swap double quotes for single quotes in json responses

:Release Notes:
Swap double quotes for single quotes in json responses

:Detailed Notes:
Using double quotes inside error messages resulted in broken json
responses. This is fixed.

:Testing Performed:
Validated JSON output of errors via luna-send

:QA Notes:

:Issues Addressed:
[ANG-739] SetAppProperty API returns invalid json object when any one of
parameter is missing

Open-webOS-DCO-1.0-Signed-off-by: Eric Blade <eric.blade@lge.com>

Change-Id: Icca94751ea31dda0c4e14eaf48b0dee6a4fa85c8
Reviewed-on: https://g2g.palm.com/4529
Reviewed-by: DCO Verification
Reviewed-by: Eric Blade <eric.blade@lge.com>
Tested-by: Eric Blade <eric.blade@lge.com>
Reviewed-by: Yasaswini AY <yasaswini.ay@lge.com>
Tested-by: Yasaswini AY <yasaswini.ay@lge.com>
Reviewed-by: Alan Levi <alan.levi@lge.com>