Add placeholder name linter

Add linter that ensures placeholder names are lowercase and use hyphens
instead of underscores.

Change-Id: Ic4f47c44a90f1721770eb3355df628dcd1b382d1
Reviewed-on: https://gerrit.causes.com/24415
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Joe Lencioni <joe.lencioni@causes.com>
Reviewed-by: Lann Martin <lann@causes.com>