Now that we've dropped gerrit 3.5 we can convert label functions to
submit requirements. This is required for Gerrit 3.7 but is optional
under 3.6. Eventually we'll need to do this for all of our custom labels
prior to the 3.7 upgrade.
Change-Id: I4dda45040842de76c12f36b5b6d6b5948d82077a