Use python3-libselinux on RHEL8/Centos8

[Mosibi]

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespaces from that line:

/kind api-change
/kind bug
/kind cleanup
/kind design
/kind documentation
/kind failing-test
/kind flake

/kind feature

What this PR does / why we need it:
RHEL 8 and Centos 8 default to python3 and do not have the libselinux-python package anymore. Instead of that the package python3-libselinux should be used. This ternary filter installs the right version.

Which issue(s) this PR fixes:

Fixes #5046

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

NONE

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[Mosibi]

/assign @riverzhang

[Mosibi]

/retest

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@Mosibi: Cannot trigger testing until a trusted user reviews the PR and leaves an /ok-to-test message.

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/retest

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[Mosibi]

Build packet_ubuntu-contiv-sep failed because it could not connect to instance-3

fatal: [instance-3 -> localhost]: FAILED! => {"changed": false, "elapsed": 240, "msg": "Timeout when waiting for 172.30.72.13:22"}

I can't think of any reason why this PR could have caused this, so i think it was an error with the test environment that's out of scope of this PR.

[riverzhang]

@Mosibi Thanks
/lgtm
/approve

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Mosibi, riverzhang

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[champtar]

Just tried it on CentOS 8 and this is not working because bootstrap-os is running with gather_facts: false

TASK [bootstrap-os : debug] ******************************************************************************************************************************************************************************************************************
Tuesday 24 September 2019  17:15:08 -0700 (0:00:00.039)       0:00:01.862 ***** 
ok: [etienne-ks147] => {
    "ansible_facts": {
        "discovered_interpreter_python": "/usr/libexec/platform-python"
    }
}

TASK [bootstrap-os : Install libselinux python package] **************************************************************************************************************************************************************************************
Tuesday 24 September 2019  17:15:08 -0700 (0:00:00.044)       0:00:01.906 ***** 
fatal: [etienne-ks147]: FAILED! => {"changed": false, "failures": ["No package libselinux-python available."], "msg": "Failed to install some of the specified packages", "rc": 1, "results": []}

kubespray/cluster.yml

Line 24 in 023108a

gather_facts: false