Previously, the role would set the host IP if a target
would only define an IPv4 address (f.ex.) and set the
IPv6 address to the host IP, which can be wrong.
Because the `blockinfile` module from ansible expects the `marker`
string to include `{mark}` case-sensetive, the entire block was
duplicated with each run.
Adds an ansible role which deploys the redis image from the docker
default library in a container, maps the data directory to the host and
uses a config which instructs redis to use a global password for AUTH.
With `redis_prefix`, a prefix can be specified to isolate multiple
instances on the same host.With a prefix like "matrix_", the user,
container-name and host data-directories get prefixed.
