Update compatibility-matrix

[ahmedwaleedmalik]

What this PR does / why we need it:
Minor updates to the compatibility-matrix

• GCE doesn't support RHEL
• Openstack has support for flatcar

Which issue(s) this PR fixes (optional, in fixes #<issue number> format, will close the issue(s) when PR gets merged):
Fixes #

Special notes for your reviewer:

Optional Release Note:

NONE

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ahmedwaleedmalik

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[kubermatic-bot]

@ahmedwaleedmalik: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-machine-controller-e2e-vsphere-resource-pool	151f075	link	true	/test pull-machine-controller-e2e-vsphere-resource-pool
pull-machine-controller-e2e-vsphere	151f075	link	true	/test pull-machine-controller-e2e-vsphere

Full PR test history

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[embik]

Should we maybe use this opportunity to remove Container Linux from the matrix? I don't think we support it at all anymore, do we?

[ahmedwaleedmalik]

Removed @embik

[kubermatic-bot]

LGTM label has been added.

Git tree hash: 4f73bc6e82ddc26da1d2fe06ba01e2308e2a9a28