Like frontend and backend options, encryption for memcached
connections is configured using tls keyword in
tls-session-cache-memcached and tls-ticket-key-memcached options.
tls-session-cache-memcached-tls and tls-ticket-key-memcached-tls
options are deprecated.

This change allows user to disable TLS per frontend address using
no-tls keyword in --frontend option.  We removed --frontend-no-tls in
favor of this new feature.

We added "tls" parameter to --backend option to enable TLS on that
backend connection.  --backend-tls options was deprecated, now is
noop.

This reverts commit 6680d8b7.