webos-image: Update for change in format of SetEnvInit.conf

:Release Notes:
As of starfish-initscripts submission 40, the format for how 
ROOTFS_READ_ONLY is set changed in SetEnvInit.conf.

:Detailed Notes:

:Testing Performed:
Built and booted target successfully.
miniBAT run - results attached to GF-39256

:QA Notes:

:Issues Addressed:
[GF-38599] Upstart: modify initctl's set-env command to process more
           than one argument
[GF-39256] CCC: Update webos-image.bbclass for change in format of 
           SetEnvInit.conf

Open-webOS-DCO-1.0-Signed-off-by: Iyad Qumei <iyad.qumei@lge.com>

Change-Id: Ia629932f2219fa0a8f138b11d1f6a3f76433d3ea
Reviewed-on: https://g2g.palm.com/3487
Reviewed-by: Susan Montooth <susan.montooth@lge.com>
Tested-by: Susan Montooth <susan.montooth@lge.com>
Reviewed-by: Jongho Kim <jongho1208.kim@lge.com>
Tested-by: Jongho Kim <jongho1208.kim@lge.com>