[crypto] Encode unicode strings in _cypherer()
pycrypto accept both bytes or string but pycryptodome, which will be introduced
in next changeset, doesn't accept this.
For backward compatibility, encode unicode strings in _cypherer()
[main]
cubicweb.session.secret = %(secret_1)s
cubicweb.auth.authtkt.session.secret = %(secret_2)s
cubicweb.auth.authtkt.persistent.secret = %(secret_3)s
cubicweb.auth.authtkt.session.secure = no
cubicweb.auth.authtkt.persistent.secure = no