weboslayers: Use AUTOREV for meta-webos

* until previewbuildscript branch is used for official builds we
  don't want to repin meta-webos every time when master branch does

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@lge.com>
gitignore: Update to ignore all meta-* checkouts

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@lge.com>