Allow for concurrency when calling CloudWatch API

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## Problem

The CloudWatch API is potentially a blocking call (even more so since we're having to lookup the last set value for the specified metric - that's if the user hasn't provided a specific value to be set - and then decide whether the value should be incremented or reset to zero, depending on if a value had been set within the last hour).

## Solution

Thread it.
Use the new Ruby 1.9 hash syntax.