Added check for dest folder in convert() api

:Release Notes:
1.Did the validation for the destination path
2.If the path does not exist created the path
3.If the path cannot be created given an error message

:Detailed Notes:

:Testing Performed:
Compiled locally and tested in device

:QA Notes:

:Issues Addressed:
[GF-10940] Passing invalid destination argument returns successful
conversion in api wallpaper/convert

Open-webOS-DCO-1.0-Signed-off-by: Yasaswini A Y <yasaswini.ay@lge.com>

Change-Id: Ib581219f3050af5bea50f69d9ad52f977b4e0714
Reviewed-on: https://g2g.palm.com/3585
Reviewed-by: Build Verification
Tested-by: Yasaswini AY <yasaswini.ay@lge.com>
Tested-by: Shrinivas Kulkarni <shrinivas.kulkarni@lge.com>
Reviewed-by: Roger Stringer <roger.stringer@lge.com>