Add support for explicit TLS 1.1 and 1.2

Add support for explicit TLS 1.1 and 1.2

Add SslProtocol enums TlsV1_1 and TlsV1_2 and use the appropriate OpenSSL
methods when they're selected (TLSv1_1_client_method, TLSv1_2_client_method,
TLSv1_1_server_method and TLSv1_2_server_method). This allows us to
explicitly use TLS 1.1 or 1.2.

Task-number: QTBUG-26866
Change-Id: I159da548546fa746c20e9e96bc0e5b785e4e761b
Reviewed-by: Richard J. Moore <rich@kde.org>
Reviewed-by: Shane Kearns <shane.kearns@accenture.com>