Add customisation hooks for various stages of jclouds machine provisioning
jclouds customization hooks: incorporate review comments

- Marks JcloudsLocationCustomizer as @Beta
- Adds BasicJcloudsLocationCustomizer
Merge pull request #1 from aledsage/jclouds-location-customizer

jclouds customization hooks: incorporate review comments
Merge pull request #431 from alasdairhodge/jclouds-location-customizer

Add customisation hooks for various stages of jclouds machine provisioning