Windows: network autotests are unreliable

There are some network autotests that are unstable or just don't work on some environments. For example:

• tst_QHttpNetworkConnection::getMultipleWithPipeliningAndMultiplePriorities() - passes occasionally but fails most of the time.
• tst_QDnsLookup - multiple failures. Fails always for me, but apparently passes for others. (RESOLVED)
• tst_QHostInfo - multiple failures. Fails always for me, but passes for others. Probably same underlying cause as tst_QDnsLookup. (RESOLVED)
• tst_QTcpSocket::disconnectWhileLookingUp - Failed at least once, but passes usually.
• tst_QTcpSocket - This test also has other consistent failures on my environment that didn't happen for others, while they reported socketDescriptor and blockingIMAP cases failing which passed for me.
• tst_QTcpServer::ipv6ServerMapped(WithoutProxy) - Fails for me always.

Of course there can be other unstable tests.

In any case, for now the 'check' target generation for network autotests has been disabled in auto.pro. The network tests need to be run in actual CI environment and if the reliability is deemed good enough, then they can be re-enabled.