QtIFW

Fix broken random name generation for temporary directories.

Task-number: QTIFW-354

The function was correctly calculating the initial part of the
name using QTemporaryFile, though the appended "meta" was not
checked and could result in duplicated names later on.

Change-Id: I00eeebbb01fbfcc5a626e4bdfe04013f8e520ed5
Reviewed-by: Niels Weber <niels.weber@digia.com>
Reviewed-by: Tim Jenssen <tim.jenssen@digia.com>