webos_version: Split by ';branch=' a bit sooner

:Release Notes:
PV was parsed incorrectly when WEBOS_VERSION didn't have any
underscore. This change also fixes branch parameters with dash
or underscore in name, which were parsed as submission/sha-1
separator.

:Detailed Notes:

:Testing Performed:
Only build tested.

:QA Notes:
No change to image.

:Issues Addressed:
[ES-862] Clarify documentation for creating pre-submission builds

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@lge.com>
Change-Id: I95f48e293ad3350b654495f436e2dd08f9f6814d
Reviewed-on: https://g2g.palm.com/5662
Build: Martin Jansa <Martin.Jansa@lge.com>
Reviewed-by: Martin Jansa <Martin.Jansa@lge.com>
Tested-by: Martin Jansa <Martin.Jansa@lge.com>
Reviewed-by: DCO Verification
Reviewed-by: Build Verification