AngularJS: MB-11954: existing default bucket during wizard setup

Change-Id: If2f00b95a4b232c7b7744c58ccbaa61641ec6b01
Reviewed-on: http://review.couchbase.org/40619
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>