Tidy impl of location.newSubLocation

- deprecate LocationCreationUtils
- use LocationSpec (e.g. in JcloudsLocation)
Add AvailabilityZoneExtension (including aws impl)
Add InterAvailabilityZoneDynamicCluster
Cassandra sample app tidy
fix name in SingleWebServerExample
Merge InterAvailabilityZoneDynamicCluster and DynamicCluster

- make DynamicCluster configurable, to do inter-availability zones
Fix ServiceReplacerTest

- change to FailingEntity had caused the "start" to be recorded in
  callHistory twice.
Fix timing in EntityConfigMapUsageLegacyTest
Merge pull request #970 from aledsage/feature/cluster-across-availabilityZones

Feature: DynamicCluster across availability zones