Make SslContext creation more flexible

[acogoluegnes]

E.g. allow to have a SslContext created for each connection of the same ConnectionFactory.

See https://groups.google.com/d/msg/rabbitmq-users/Jl5ffHgueDw/1bUsPxzYEAAJ.

[acogoluegnes]

This would typically require API changes, e.g. in FrameHandlerFactory.

[vibhuyadav]

This would be a great addition