Ensure GCE disk name does not start with a number

[justinsb]

As this could not have worked before, we don't have to worry about
compatability with existing users.

[KashifSaadat]

LGTM. Just curious, as the ClusterSpec isn't updated and you're prefixing the volume name with a letter, would subsequent cluster updates detect the EtcdMemberSpec is different to what resources are created and attempt to re-create?

[justinsb]

Thanks @KashifSaadat . I believe it would not - this is mapping from the kops model -> the GCE model. As long as the GCE model always has the same name, I believe we should be fine. So we just added an extra rule in the kops -> GCE rule, which is that if it starts with a number, we start with the letter 'd'. That would be a breaking change, except that disks that started with a number previously would have failed.

/retest

[justinsb]

Makefile woes

/retest

[KashifSaadat]

Ok great :)

/lgtm

[k8s-ci-robot]

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