snap: ensure that plug and slot names are unique

[zyga]

This branch extended snap validation to ensure that plug and slot names are unique within one snap so that a given name is always uniquely identifying a plug or a slot but not both.

Signed-off-by: Zygmunt Krynicki zygmunt.krynicki@canonical.com

[niemeyer]

LGTM. Let's just wait for tests.

[jdstrand]

Hrmmm, I'm curious about the motivation for this. For example, the docker snap was going to use:

apps:
  docker:
    command: docker-wrapper docker
    plugs:
      - docker
      - network
      - home

  dockerd:
    command: dockerd-wrapper
    daemon: simple
    plugs:
      - network-bind
      - firewall-control
    slots:
      - docker

In this manner we wouldn't have a 'docker-client' interface and a 'docker' interface, but could just use one for each.

This can be worked around with:

plugs:
  docker-cli:
    interface: docker
slots:
  docker-daemon:
    interface: docker

apps:
  docker:
    command: command-docker.wrapper
    plugs:
    - docker-cli
    - network
    - home
  dockerd:
    command: command-dockerd.wrapper
    daemon: simple
    plugs:
    - network-bind
    - firewall-control
    slots:
    - docker-daemon

but I don't understand the point of the PR if this is supposed to work. I'll discuss on IRC.