Add a job that will propose a change (or update a change) to
normalize projects.yaml, and run it once daily. Normalization,
in this case, chiefly means removing un-used upstream lines
from projects.yaml (but will also catch minor YAML errors and
line wrapping).
Also simplify the proposal node regex.
Change-Id: I6520dfcd6f523886aba352f9bd7f9186cfeed84a