separate machine tools from individual container tools

[William Reade]

<capturing lisbon discussion & agreement>

At the moment we have:

/var/lib/juju/
- tools/
  - v1/
  - v2/
  - machine-0 -> ./v2
  - principal-0 -> ./v1
  - subordinate-0 -> ./v1
- agents/
  - unit-principal-0/
    - <unit stuff>
  - unit-subordinate-0/
    - <unit stuff>

...but this mixes stuff-in-container with stuff-outside-container. We should actually have:

/var/lib/juju/
- tools/
  - v1/
  - v2/
  - machine-0 -> ./v2
- containers/
  - unit-principal-0/
    - tools/
      - v1/
      - unit-principal-0 -> ./v1
      - unit-subordinate-0 -> ./v1
    - units/
      - unit-principal-0/
        - <unit stuff>
      - unit-subordinate-0/
        - <unit stuff>

...and ensure that the machiner, when it deploys a new container, actually *copies* its tools into the container; this chroot-without-actually-chrooting style will make it much easier to switch over to *isolated* containers when the time comes.

[William Reade (fwereade)]

Justification no longer valid: we have a Deployer interface that can easily wrap LXC deployments when required (which will surely require their own tools). When we have LXC deployments, they will surely require their own tools; but while we don't, there's no benefit in a subtly-tweaked alternate Deployer for principals.