webos-image.bbclass: Add luna-service2-disable-security IMAGE_FEATURE

:Release Notes:
Luna-service2 security features can be disabled by adding
"luna-service2-disable-security" to IMAGE_FEATURES.

:Detailed Notes:

:Testing Performed:
Verified applying of luna-service2-disable-security feature in build.

:QA Notes:

:Build Notes:
Needs to be merged together with
https://gpro.palm.com/10681

:Issues Addressed:
[GF-2826]  Add luna-service2-disable-security IMAGE_FEATURE
[GF-37370] CCC: Add luna-service2-disable-security IMAGE_FEATURE
Change-Id: I8f9586289014e8f6e39556191b69832145cf9eea
Reviewed-on: https://g2g.palm.com/3347
Reviewed-by: Herb Kuta <herb.kuta@lge.com>
Tested-by: Herb Kuta <herb.kuta@lge.com>
Reviewed-by: Susan Montooth <susan.montooth@lge.com>