Don't include by default ciphers that are not supported

There could be cases (mostly when compiled on old systems, since modern
openssl versions don't include such insecure ciphers) in which
defaultCiphers included a cipher that wasn't in the supported ciphers
list. With this patch we make sure that defaultCiphers is a subset of
supportedCiphers

Change-Id: I545ea21f5fd3a6ed13b366cdd56a1393233f9fc9
Reviewed-by: Richard J. Moore <rich@kde.org>