2e1455c4a100170c322165af3ecbbcd3004b2f9d Replace obsolete functions of QSslSocket (Hennadii Stepanov)
Pull request description:
The [QSslSocket::setDefaultCaCertificates()](https://doc.qt.io/qt-5/qsslsocket-obsolete.html#setDefaultCaCertificates) and [QSslSocket::systemCaCertificates()](https://doc.qt.io/qt-5/qsslsocket-obsolete.html#systemCaCertificates) member functions are obsolete since Qt 5.12.
This PR replaces them, does not change behavior and keeps compatibility with Qt 5.5.1.
This is a backport of Core PR16708