Check CloudHSM support selected subnets/AZs prior to creating cluster

In Regions where more than 3 AZs exist, CloudHSM might not be supported in all AZs. Currently, the template may either encounter an unsupported AZ during creation of the first HSM or during creation of subsequent HSMs. In the latter case, there can be a delay of minutes prior to recognition that an unsupported subnet/AZ has been specified.

Ideally, the template would check up front the specified AZs and issue an error prior to creation of the first HSM when an unsupported subnet/AZ has been specified.