Modify command logkv

:Release Notes:
The command logkv can log without kv-pair.

:Detailed Notes:
If when do logkv, it was accecpting atleast one kv-pair.
The kv-pair should be optional, so modify this routine.

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

:QA Notes:

:Issues Addressed:
[GF-13252] pmlogctl expects atleast one key-value pair in logkv

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

Change-Id: Id6f00e515b5ec3f90132a720afc68dac87c112c3
Reviewed-on: https://g2g.palm.com/3079
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>