Get away from master/slave phrasing

[bopopescu]

For diversity reasons, it would be nice to try to avoid 'master' and 'slave' terminology in this repository which can be associated to slavery. The master-slave terminology could be problematic for people in several countries which has the history of slavery like Romania, USA and many others. Thank you for considering the proposal. Let me know if any changes in the PR are needed, I would be happy to implement them.

[shlomi-noach]

Hi @bopopescu , please note that this repo has been superseded by https://github.com/openark/orchestrator where active development takes place. This repo is stale. I see you also opened a PR at openark/orchestrator, let's continue the discussion there.