Fix race in NewUUID()

[AstolfoKawaii]

Fixes race in NewUUID() (non-synchronized access to nodeID)

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[AstolfoKawaii]

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[pborman]

Thank you for pointing this out. The expectation was the nodeID would only ever be set once as the standard implies it is a fixed value per machine. But you are right, there is a race condition. See my comment below about just moving some code around to get the same effect.

[pborman]

Thank you.