Change default linux backends when dbus is not present
Change default linux backends when dbus is not present

Change the default linux backend to unix when dbus isn't
present.  This is a better backend to default to than
the localsocket backend since it doesn't spin the Qt
event loop.

Change-Id: I7af9bf588504ee82c8269a76a7cbd0ff123df042
Reviewed-by: Lincoln Ramsay
Reviewed-by: Jonas Rabbe <6e9178b26dba0cd114a9aed0874c56cbbaba6438@gmail.com>

qtproject/qtsystems,qtproject/qtsystems