Add Subject Key Id field to CA certificate

[qinqon]

What this PR does / why we need it:
The SKI field is mandatory for CA certificates, but Go crypto library for versions < 1.15
is not filling in the SKI field for CAs [1] this PR replicate the golang >= 1.15 fix [2].

Replicated from qinqon/kube-admission-webhook#42

[1] golang/go#26676
[2] https://go-review.googlesource.com/c/go/+/227098/

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 #

Special notes for your reviewer:

Release note:

Add SKI field to CA certificate

[kubevirt-bot]

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[kubevirt-bot]

@qinqon: The following test failed, say /retest to rerun all failed tests:

Test name	Commit	Details	Rerun command
pull-kubevirt-e2e-k8s-1.18	46993a9	link	/test pull-kubevirt-e2e-k8s-1.18

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