Don't send "none" as security type for open networks

:Release Notes:
Send empty list instead of "none" for open networks.

:Detailed Notes:
webos-connman-adapter should not report "none" as security when a network
does not have any security configured. It should just report a empty list
 for the availableSecurityTypes argument. This change removes "none" as
a security type, since Open webOS luna-sysmgr doesn't recognize "none".

:Testing Performed:
Verified that com.palm.wifi/findnetworks doesn't return security type
"none" for open networks.

:Issues Addressed:
[BHV-69] webos-connman-adapter reports "none" as security type for wifi
         networks without security

Open-webOS-DCO-1.0-Signed-off-by: Sapna Todwal <sapna.todwal@lge.com>

Change-Id: I4bbe370d70c5e2a6555340ca68e6a9b2a378b406
Reviewed-on: https://g2g.palm.com/4751
Reviewed-by: DCO Verification
Reviewed-by: Simon Busch <simon.busch@lge.com>
Reviewed-by: Sapna Todwal <sapna.todwal@lge.com>
Tested-by: Sapna Todwal <sapna.todwal@lge.com>