Use Hash by default, so attributes are overridable.

Arrays aren’t very good in Chef, due to not being
able to merge individual items. Changing to Hash
named pools means node attribute precedence can
override attribute values, which is important for
DRY definitions.

Arrays are still supported for BC.
Use ruby 1.8 style Hash =>
Merge pull request #1 from andytson/feature/named-pools

Use Hash by default, so attributes are overridable.