Refactor the CDT Core CommandLauncherFactory extension

- clean up the extension to have a simple
  factory element with id, priority, and class
- have CommandLauncherManager use the priority
  of factories to find the best launcher
  (one returned by factory with highest
  priority or first one returned by factories
  of equal priority)
- fix the specification of the Docker Container
  Command launcher in org.eclipse.cdt.docker.launcher
  plug-in
- fix CModelMock to return an ICProjectDescription so
  serializer tests will work with CommandLaunchManager

Change-Id: I91c383c1f4da05b9c39fefceb0bea572fb4af34b
4 files changed