Spotinst: Do not log unmatched groups as warning messages

[liranp]

When executing kops rolling-update cluster without instance group name/role, if the user has multiple Elastigroups that aren't managed by kops, kops prints a lot of less than worthwhile warning messages:

W1030 21:29:37.226502 21141 resources.go:109] Found group with no corresponding instance group "name-of-the-elastigroup"

This PR changes the logging level from Warning to Info.

[KashifSaadat]

Hey @liranp, thanks for the contribution!

The GetCloudGroups function accepts a bool for warnUnmatched so it is probably better to look at where this is called in the code and update there, e.g. : https://github.com/kubernetes/kops/blob/1.11.0-alpha.1/cmd/kops/rollingupdatecluster.go#L269

Unless you think in all cases (for the supported cloud providers / different implementations) the log line should be downgraded, in which case warnUnmatched should be removed altogether. @justinsb what do you think?

[liranp]

@KashifSaadat You're right, but there's no way to toggle the warnUnmatched boolean off when the rolling-update command is executed against the whole cluster.

[justinsb]

Oh - this is in the spotinst code, not the general AWS code. In that case it's fine by me.

I think for general AWS we do some tag filtering (so we only match ASGs that are tagged to this cluster), so this is more surprising in the general AWS case - and justifies a warning. If you can do similar filtering, I would recommend doing that and keeping it as a warning.

But ... if you choose to do that, it can be a follow-on PR.

Thanks @liranp

(PS and thanks @KashifSaadat for thinking through the implications)

/approve
/lgtm

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