[feature/dao] cassandra authentication + client encryption

[thibaultcha]

This PR addresses #373 (Cassandra authentication). Kong can now be used with any authenticated/encrypted Cassandra cluster (ie. instaclustr.com).

In order to do this and as an investment for Cassandra related features to move faster in the future, the Cassandra driver was switched from jbochi/lua-resty-cassandra to a new one, which supports both binary protocols v2 and v3, as well as authentication and client encryption.

Changes

• Cassandra driver (lua-cassandra) now uses binary protocol v3. This in an investment in order to improve the DAO in the future, and use some of the new features provided by the v3 protocol (ie. named values binding).
• Support for authentication (PasswordAuthenticator).
• Support for client-to-node encryption.

The driver supports all those features for both Luasocket and OpenResty environments. For it to work in Kong, this is the changes one would have to make to their configuration file:

databases_available:
  cassandra:
  properties:
    ssl: true # for client-to-node encryption
    ssl_verify: true # if SSL verification
    ssl_certificate: "/path/to/cluster-ca-certificate.pem" # **absolute** path to the certificate authority file
    user: cassandra # user (and password) if the cluster has authentication enabled
    password: cassandra
    #  [...]

This makes Kong fully compatible with Cassandra provisioning services such as https://www.instaclustr.com.

I would recommend not merging this for the upcoming 0.4.0 since the switch of the underlying Cassandra driver is a potential breaking change. This could be part of an eventual 0.4.1 or 0.5.0 (in a shorter time span then 0.3.2 -> 0.4.0).

[thibaultcha]

Merging this to start testing it + I'll need it for an upcoming fix about the DAO in plugins-migrations.