Change default target from stable/icehouse to master
Change default target from stable/icehouse to master

As of writing this commit message icehouse has yet to be released so
stable/icehouse doesn't exist.  So make the default values the same as
how we use grenade in gate.

Change-Id: I6102c67b6c0021ccd9d7ec540cc1510491f88eb2

dtroyer/grenade,openstack-dev/grenade,openstack-dev/grenade,dtroyer/grenade