example open loop policy

Builds on https://github.com/brooklyncentral/brooklyn/pull/514, so please review and merge that first. I can then rebase for any changes required in that pull request.

This provides a new example (primarily for demos) that detects when the AutoScaler policy has reached its max pool size (i.e. it wants to increase the pool size, but the cap forbids that). It then sends an SMS message to notify an operator.