[Twisted-Python] Specifying ciphers in ssl.optionsForClientTLS

[Jason J. W. Williams]

> As the documentation for extraCertificateOptions says, if you need to use it it's a bug in the interface.  As such, please file it :-).  This escape-hatch was presented specifically so we could discover which features of that interface were really necessary customizations and which were just unfortunate compromises with OpenSSL's API.

Reported: https://twistedmatrix.com/trac/ticket/7792