QtIFW

When running sudo'ed process, make reading from child non-blocking

For some reason, using a blocking read would sometimes(!) not cause the
sudo process to finish. In fact, it didn't even seem to start running,
even though it showed up in the process list. Maybe a deadlock? Using
non-blocking reads fixes this.

Change-Id: Ic8a94b38e4be426abcc08bbd0dd887a3cffda5d5
Task-number: QTIFW-771
Reviewed-by: Katja Marttila <katja.marttila@theqtcompany.com>