Stop using #include <QtTest> in Qt tests

To use QtTest the correct include is QTest or QtTest/QTest.

All other things being equal, it's NOT correct to use QtTest or QtTest/QtTest, as those are the module-wide includes, which recursively include all of QtCore  plus other files (e.g. QtGui stuff).

There are as of now some 600+ occurences of QtTest inclusions in qtbase tests alone.

1. Has anyone tried to do a mass search and replace and compare the build times?
2. How about having the sanity bot automatically flag any usage of module-wide include?