Validation json data for kv-pairs

:Release Notes:
PmLogString() validates kv-pair whether json data is acceptable

:Detailed Notes:
Now, PmLogString is using pbnjson's jsax_parse to validate json
data for kv-pairs.
It'll return error and record error text in /var/log/legacy-log.

:Testing Performed:
Compiled locally and tested on local and TV.
Verified in the log file, error text displayed in
/var/log/legacy-log properly.

:QA Notes:

:Issues Addressed:
[GF-10703] pmloglib: Add json string check in PmLogString API

Open-webOS-DCO-1.0-Signed-off-by: Hongjeon Ha <hj.ha@lge.com>

Change-Id: I3aca79593db2733042c6f45d0bb6dd6873311729
Reviewed-on: https://g2g.palm.com/2903
Reviewed-by: Build Verification
Reviewed-by: Hongjeon Ha <hj.ha@lge.com>
Tested-by: Hongjeon Ha <hj.ha@lge.com>
Reviewed-by: Gayathri Srinivasan <gayathri.srinivasan@lge.com>
Reviewed-by: Keith Derrick <keith.derrick@lge.com>