XenServerIPv6

Summary
Create interface templates / file injections for adding IPv6 addresses and routes to XenServer instances.

Release Note
Provides users native IPv6 access on their XenServer instances.

Rationale
IPv4 is running out. We need to support IPv6.

User stories
John wants to provide IPv6 services on his instance. He will be automatically assigned a /NN block per instance and have the ability to add as many IPv6 addresses as his heart desires.

Design
The overall idea is to use the agent to inject networking rules to the instance based off of the distro -- same as IPv4. Each distro will have their own set of interface templates that will be used to bring up the interface. We'll pass along a pre-generated IPv6 address and its default route.

UI Changes
n/a

Code Changes
Will likely only require additional interface templates.

Migration
n/a