Open the dummy device for tests on any platform
Open the dummy device for tests on any platform

The virtual serial port drivers (such as com0com or tty0tty)
require all pairs of devices were open, otherwise any
I/O will fails. Seems, it is feature of com0com and tty0tty
drivers, and maybe others drivers of virtual devices.

There is only one waitForReadyReadWithTimeout() test which
opens the dummy device only in Windows. So, it is necessary
to open the dummy device on any platform.

(cherry-picked from 7fbc7cefcada03aa455bda305734663cf2b6a117)
Change-Id: I472238704fe200309b5015c2f9740d8e4b6cb41f
Reviewed-by: Denis Shienkov <6a9c747bd2ba446682324cf340d3b86f30cf4d55@gmail.com>

RoadWorksSoftware/QtSerialPort-OS2,RoadWorksSoftware/QtSerialPort-OS2