Nested event loops are dangerous and in this case lead to a crash.
So change the api of ensureConfigured to not use a nested event loop.
The CustomExecutableRunConfiguration then has to manage the dialog more
explicitly. Also this makes the dialog non modal, since it should then
cope with every situation.

Task-number: QTCREATORBUG-11416
Change-Id: I2af782915c148f8dff1b0df54fdb64aa83f684d2
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>