Qt 5.6/Windows: Test qtdeclarative\tests\auto\qml\debugger\qqmldebuglocal asserts/fails

See https://codereview.qt-project.org/#/c/153638/

Suspicion so far is that sth broke in QLocalSocket.

The debugger tries to write sth onto the local socket in signal newConnection(), which fails.

Assert is:

FATAL : tst_QQmlDebugLocal::initTestCase() ASSERT: "writeBytes == p.b.size()" in file ..\..\..\..\..\src\plugins\qmltooling\shared\qpacketprotocol.cpp, line 289

Introduced by "Make QWindowsPipeWriter thread-free." 0307c008bf71e1272385d0e7f7c8d2c5a1ba6526 (https://codereview.qt-project.org/#/c/152304/ )