Handle SELinux on FCOS and Enterprise Linux.

[OrvilleQ]

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Relate to #428

It seems like if we upload custom binary to CoreOS, ~the binary path defined in k0sctl for CoreOS (/opt/bin/k0s) will be ignore,~(Not sure if this is the reason) result to Failed at step EXEC spawning... Permission denied error which seems to be selinux reject systemd to execute the binary.

Will provide more detail later.