Change default branches for Dizzy in preparation for 1.7

The only project still using master is Meta-OpenEmbedded as
it still does not provide a dizzy branch. This ought to
be changed once it does.

Change-Id: I91b6f8f49c02a5d41305cf6896215fbd253f92b7
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>