Qbs: Wait for reparsing to be done after a build

This is necessary since the build may change the the properties of
the build targets (executable name, etc.), so we can not proceed
to run anything without that update.

Change-Id: I9790c529db5e4da61f59e638a05339ada714353c
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>