New playbook backend + flag fixes

[chungers]

This PR

• adds a new controllerCommit backend for controller specs as playbooks
• fixes logic for handling missing float/int/bool param/flag values
• fixes a problem with pool controller's fsm stuck in "provisionFail" state when it's only the client api timed out during provision (e.g. when provisioning a spot instance which takes a while and can cause ec2 api client to timeout).

Signed-off-by: David Chung david.chung@docker.com

[GordonTheTurtle]

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

$ git clone -b "0409-fixes" git@github.com:chungers/infrakit.git somewhere
$ cd somewhere
$ git rebase -i HEAD~842360409312
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.