prepare-submission.sh: Add --no-merges option to git log (v1.0.2)

:Release Notes:
Output for :Detailed Notes: shouldn't show merge commits.

:Detailed Notes:

:Testing Performed:
Only build tested.

:QA Notes:
No change to image.

:Issues Addressed:
[ES-925] prepare-submission.sh: Output for :Detailed Notes: shows merge
         commits

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@lge.com>
Change-Id: I8ec716d588ca5aee26d958632d4b50c13e588b30
Originally-reviewed-on: https://gpro.palm.com/58813
Reviewed-on: https://g2g.palm.com/6424
Reviewed-by: Martin Jansa <Martin.Jansa@lge.com>
Tested-by: Martin Jansa <Martin.Jansa@lge.com>
Reviewed-by: Susan Montooth <susan.montooth@lge.com>