Add support for running multi-node tests inside docker containers

[kpritam]

We have been migrating our build environment to openshift(kubernetes) but we have a bunch of multi-node tests which currently runs across physical machines on aws.

And looking at the current trends in industry, lot of people are moving towards kubernetes and containers.
So it would be really beneficial to add support for containers in multi-node testkit.

[ktoso]

If you'd like to contribute such support feel free to do so.
The tool is mostly used for our own testing, and currently fits our needs so we're not looking to build much more infrastructure into it right now (may change in the future, but not now)