Windows: Fixed helper process finding in network tests

Windows: Fixed helper process finding in network tests

Helper processes were not found properly on all network tests
when the test was run with "nmake check":

- tst_qtcpsocket
- tst_qtcpserver
- tst_qnetworksession
- tst_qnetworkreply

Task-number: QTBUG-24199
Task-number: QTBUG-24203
Task-number: QTBUG-24226
Task-number: QTBUG-24231
Task-number: QTBUG-24232

Change-Id: Ia4451b5a5e3fe9f81aba3837baf8292411f995d8
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@nokia.com>
Reviewed-by: Shane Kearns <ext-shane.2.kearns@nokia.com>