End to end tests now includes the manager

[chungers]

The tutorial and container tests in the scripts directory are good end-to-end tests that verify plugin-to-plugin communications/protocol and group controller's functionality. This PR adds the manager in the suite of plugins:

• Note it is now the first to be started --- the manager no longer has a startup dependency on another group (stateless) plugin
• The user's specification is now persisted on-disk (see the configs directory) thanks to the manager.
• A file-based leader detection mechanism is used.

[GordonTheTurtle]

Please sign your commits following these rules:
https://github.com/docker/docker/blob/master/CONTRIBUTING.md#sign-your-work
The easiest way to do this is to amend the last commit:

$ git clone -b "manager-tests2" git@github.com:chungers/infrakit.git somewhere
$ cd somewhere
$ git rebase -i HEAD~842353495432
editor opens
change each 'pick' to 'edit'
save the file and quit
$ git commit --amend -s --no-edit
$ git rebase --continue # and repeat the amend for each commit
$ git push -f

Amending updates the existing PR. You DO NOT need to open a new one.

[codecov-io]

Current coverage is 64.77% (diff: 100%)

Merging #355 into master will not change coverage

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  Hits           1291       1291          
  Misses          569        569          
  Partials        133        133          

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