Rework QNetworkProxyFactory::systemProxyForQuery autotest

Rework QNetworkProxyFactory::systemProxyForQuery autotest

Rather than requiring specific hardcoded proxies in the system,
it now checks the proxies returned by the system have the required
capabilities for the request.

Note the test will pass if no proxy is configured (as
QNetworkProxy::NoProxy has all required capabilities)

The test prints the returned proxy lists and elapsed time
diagnostic for manual comparison and debugging.

Change-Id: I621ef4d1d7264a98c3e8bd485c30bc1166fcbdf0
Task-number: QTBUG-19454
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>