slight changes to thunderbird meetings

[David Ascher]

In order to streamline communication between drivers and the rest of the
TB3 team, we're going to shift our meetings around a bit.

Specifically:

- drivers will meet at 9am PST (1/2h before the regular Tb meeting),
to do a quick check of where we think things are, and to prepare for the
larger meeting.
- the regular meeting will happen as usual
- the drivers will optionally have a followup meeting to deal with any
driving action-items that fall out of the regular meeting, or do bug triage.

As usual, not everyone can make these meetings, so we'll do our best to
publish notes of the important bits.

--david