webos.inc: Add the build codename to image names

:Release Notes:
Prefix WEBOS_IMAGE_NAME_SUFFIX with WEBOS_DISTRO_BUILD_CODENAME-. For
authoritative official builds, this has the effect of prefixing the
build number with the build codename.

:Detailed Notes:
Also
- Update the description of WEBOS_DISTRO_BUILD_ID to correspond to how
  it's currently being set.
- Have the value of WEBOS_IMAGE_NAME_SUFFIX include the leading hyphen
  so if other distros don't want to use it, the image filenames won't
  contain doubled hyphens.

:Testing Performed:
Confirmed using:
  $ bitbake -e starfish-flash | grep 'IMAGE_NAME='
that the of value is as expected.

:QA Notes:

:Issues Addressed:
[GF-57864] Add the build codename to the image names for branch builds
[GF-58280] CCC: Add support for branch builds

Open-webOS-DCO-1.0-Signed-off-by: Herb Kuta <herb.kuta@lge.com>

Change-Id: I44f950962079c812542270fb6e09472d6a61ad7c
Originally-reviewed-on: https://g2g.palm.com/4375
Cherry-picked-from-commit: 132a9980bac2b876cebd1a79e138d7e478fd74c1
Cherry-picked-from-branch: @acadia
Reviewed-on: https://g2g.palm.com/4396
Reviewed-by: DCO Verification
Build: Herb Kuta <herb.kuta@lge.com>
Reviewed-by: Herb Kuta <herb.kuta@lge.com>
Tested-by: Herb Kuta <herb.kuta@lge.com>
Reviewed-by: Build Verification
Reviewed-by: Martin Jansa <Martin.Jansa@lge.com>
Reviewed-by: Susan Montooth <susan.montooth@lge.com>