Make sure to have a hardware integration when creating windows

We need to do a full roundtrip and wait for the qt_hardware_integration
global before returning from QWaylandDisplay constructor. Waiting
for the screen is not enough, since there is no guarantee it will come
after the hardware integration global.

Change-Id: I34cb50b830632db7e5d5c7a502eeef778599b267
Reviewed-by: Gunnar Sletta <gunnar.sletta@jollamobile.com>
Merge pull request #14 from giucam/clientintegration

Make sure to have a hardware integration when creating windows