Improve N2VC performance/functionality

- Refactor test to support multi-vdu charms.
- Add support for deploying multi-vdu charms.
- Execute the initial-config-primitives

This is the first commit to add support for executing the
initial-config-primitive(s). There are some decisions that still need to
be made: how do we report primitive execution back to the
caller/callback in a meaningful way.

Signed-off-by: Adam Israel <adam.israel@canonical.com>
Change-Id: Icc0ce41d256930b337c9097af9edcae2694207e8