sslutil: move SSLContext.verify_mode value into _hostsettings...
sslutil: move SSLContext.verify_mode value into _hostsettings
_determinecertoptions() and _hostsettings() are redundant with each
other. _hostsettings() is used the flexible API we want.
We start the process of removing _determinecertoptions() by moving
some of the logic for the verify_mode value into _hostsettings().
As part of this, _determinecertoptions() now takes a settings dict
as its argument. This is technically API incompatible. But since
_determinecertoptions() came into existence a few days ago as part
of this release, I'm not flagging it as such.
