allow for nightly-date type channels

[escapewindow]

That may just be adding nightly-date (or whatever the date channel is called) to this line in puppet.

[escapewindow]

Looks like @Callek wants nightly-date pushes to production AUS to work on date again.

We may need to:

• revert https://hg.mozilla.org/projects/date/rev/c905f746641918a675cbc4799600c7336219c552
• change the channel in the date balrog tasks to be nightly-date
• allow for nightly-date in the balrog scriptworker configs

[MihaiTabara]

At this point balrogscript knows nothing of channels. We can make the necessary changes should we want to be explicit but I think it's overkill at the moment. We'll be extending balrogscript most likely to take these into account once we teach it to do rules/channels munging too, in da futurez!