Fix terraform consistent variables for machine deployment replicas

[adeniyistephen]

What type of PR is this?
Fixing terraform variables for consistency among cloud providers

What this PR does / why we need it:
To enable consistent variables among cloud providers for the machine deployment replicas.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes https://github.com/kubermatic/ps-team-flotilla/issues/99 ticket

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[stroebitzer]

Looks good to me. Please check with Artiom the following things:

• On Hetzner this would be a breaking change. Ask Artiom if that is OK, at least we have to document it in the release notes that it is a breaking change
• Please ensure that the docs are also updated. So the KubeOne docs and the examples in the KubeOne repo

[adeniyistephen]

You mean so the kubeone docs and example both rhyme with same updates?

[stroebitzer]

yes