webos.inc: Prepend scripts directory to PATH

:Release Notes:
In some cases we need to use our version of scripts in layer/scripts
instead of default version from upstream layers like oe-core.

:Detailed Notes:
For example, the newer buildhistory commits depend on backported changes
to oe-pkgdata-util.

:Testing Performed:
Only build tested and checked with bitbake -e.

:QA Notes:
No change in image.

:Issues Addressed:
[GF-13912] Fix PATH setting in the layer.conf of webOS layers

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@lge.com>
Change-Id: I3fcc9e333dd410aa9ca144e3437fa267458d709b
Reviewed-on: https://g2g.palm.com/3120
Reviewed-by: Herb Kuta <herb.kuta@lge.com>
Reviewed-by: Build Verification
Reviewed-by: Martin Jansa <Martin.Jansa@lge.com>
Tested-by: Martin Jansa <Martin.Jansa@lge.com>
Reviewed-by: Susan Montooth <susan.montooth@lge.com>