Add Docker Bench for Security

The Docker Bench for Security [1] is a script that checks for common
best-practices around deploying Docker containers. The Robot test case
added uploads the test script on all nodes of the cluster, runs all
available CIS tests and downloads produced execution logs.

[1] https://github.com/docker/docker-bench-security/tree/master

JIRA: VAL-35

Change-Id: I107673363453f38344fd9db3c88b88ea70f1074a
Signed-off-by: Juha Kosonen <juha.kosonen@nokia.com>