Add Route 53 private hosted zone support

[axelfontaine]

This would be implemented as a configuration setting like -privatezone=.... Once this is set for an environment Boxfuse would then add entries for all single-instance and load-balanced apps.

For load-balanced apps, an ALIAS record would contain the address of the ELB.

Open questions:

• Which address should be put in for single-instance apps? The private IP (which changes upon redeploy) or something like a secondary private IP (but then how should this one be assigned/picked)?
• Should this even be configured or could Boxfuse simply auto-create a private zone?
• Should this be per environment or per account (meaning one zone for all environments with the environment name embedded in the record name like for boxfuse.io)?

[vteslenko]

1) Primary private IP will work in most cases. Having a user-defined private IP will add flexibility. 2) Use existing or auto-create if it does not exist. 3) Having per-environment option will allow us to create R53 private zones and independently attach them to specific VPCs. That adds flexibility. One per account will also work in many cases though.