Bump kazoo version to 2.6.0 that supports SSL.
Allow to configure ssl config options via conf
* keyfile
* keyfile_password
* certfile
* use_ssl
* verify_certs
https://kazoo.readthedocs.io/en/latest/api/client.html#kazoo.client.KazooClient
This should be done in conformance with Redis
jobboard backend, that already allows SSL settings.
Change-Id: Ic2670c3c4caa93f69bc2d541c3701df2b6037d2e