TestBench: add isDefault property.
TestBench: add isDefault property.

Change-Id: Ic05275142809c113418aa1ae0b0717f88b6e6b35
Reviewed-by: Jens Bache-Wiig <9cea9d70b08f8210134ec5959114f72bad51ed1d@digia.com>

drgvond/qtquickcontrols,kobolabs/qtquickcontrols,drgvond/qtquickcontrols,kobolabs/qtquickcontrols,mizukusak/qtquickcontrols,mizukusak/qtquickcontrols,kobolabs/qtquickcontrols,drgvond/qtquickcontrols,mizukusak/qtquickcontrols